Battery consumption of a fridge?

[MapisM]

I’m thinking of the Lifelines and hoping to get a deal if buying 8 of them.

Do you already have a supplier in mind to ask a quotation, J?
I might throw in my batteries as well, and see what they come up with.
Though unfortunately I have a 400mm length constraint, so I can't use the 520mm long batteries.
The racks on my boat were built for the square shaped Exide NG-2, some huge FLA 280Ah batteries weighing as much as myself.
I don't think they are used in anything else than fishing boats nowadays, where they can be accessed and moved around with a crane.... :ambivalence:

 

[Trundlebug]

Out of interest, are they open/wet cells, or are they sealed batteries? And what sort of capacity is each bank? Were the scissor lift's batteries the same type / similar size?

Open lead acid, deep cycle. Here's a (very poor, sorry) picture to illustrate.
You can see the near bank of 12 cells in the foreground, and the other bank on the far side. 48v total.
Spec is 24 x 2v heavy duty 301Ah.
You can just see the small blue magic box on the top of the near bank.
If you're wondering where the rest of the cherry picker is, pic was taken whilst replacing the slew ring bearing recently.
Photo borrowed from the report so hence the poor quality.

[/URL]
Scissor lift is just a baby. 2 x 12v 80Ah Trojans now fitted.

 

[Trundlebug]

@JFM

Have you considered fitting solar panel(s) to supplement your other charging?
Given your location it could and would provide useful supplement and help the batteries considerably.
There must be room on a ship of Match II's size for at least 150-200w of panels?
Whilst I appreciate they don't help at night when you're hammering the batteries, at least they are providing charge all day long when the generator and / or engines aren't, so they could usefully provide that final (and silent) top up to the charge cycle?

I'm just about to fit a 150w semi flexible solar panel to my sunroof. Importantly it can be walked on, as I need to get up there to fold the radar arch down for low bridges etc.
Even in the UK I'm expecting a significant help to the extra consumption of my new fridge.

 

[jfm]

@Vas
May batts are not all in one tray - they are in separate trays 2+2+4 batts (actually GRP boxes with lids and hydrogen vents). So I might as well keep 2x 200Ah for each engine starter (they are monster starter motors; V12 x 32 litre engines). I will measure the domestic batt box this weekend and see what size Lifelines I can squeeze in

I wasn't making a distinction between different types of wet LA ie sealed or with open caps, as that kinda would complicate the choices/lengthen my post and tbh I am not buying wet LA anyway due to slow charge acceptance. (@MapisM, AGM is a subset of LA in my book, which is why I used the terms "wet LA" and "AGM")

I have 2 perfect wet LA sealed 220Ah, being the engine starters that have not been busted by dropping to 20v. If only I could get them to Volos you would be welcome to them foc!

The 260Ah are 70kg whereas 220Ah tend to be about 55kg (roughly)

@MapisM,
yes I have been thinking of re wiring to 6+2 instead of 4+2+2. Makes good sense and I have a parallel switch plus all sorts of other plans B incl twin gensets to charge anything that is flat. It is quite a big job cablewise because the 2+2 are port side and the 4 are starboard, but it is do-able. I'm going to think about it as a future project, but tbh 440Ah is enough for a full night of refrigeration hence it doesn't spoil my boating

I don't really get the idea of multiple 2v cells. The busbars inside the battery connecting the cells, welded on, is always going to be better than cables external to the battery isn't it? The only reason to separate batteries of cells is weight, ie 50-60kg is about the limit for handling

@Trundlebug
Yes nice solar panels would be nice. I would like to research them some more and of course the later you leave it the better the technology gets! It would be a nice thing to do and this winter I have a hardtop being fitted to the boat (more info on another thread soon; the thing is due to be delivered next week) which gives me somewhere to stick them. The HT middle opens up like a fabric sunroof but if flexi solar panels are availalbe then it gets interesting

 

[burgundyben]

Yes nice solar panels would be nice. I would like to research them some more and of course the later you leave it the better the technology gets! It would be a nice thing to do and this winter I have a hardtop being fitted to the boat (more info on another thread soon; the thing is due to be delivered next week) which gives me somewhere to stick them. The HT middle opens up like a fabric sunroof but if flexi solar panels are availalbe then it gets interesting

Interesting, a bit of augmentation via solar panels was part of my thought process, you do need a fairly bit area to make much of a difference, but as you say, longer you leave it the better the solutions become. I wonder how many cycles the rolly uppy bendy ones can survive?

 

[MapisM]

(@MapisM, AGM is a subset of LA in my book, which is why I used the terms "wet LA" and "AGM")

Agreed.
If you're referring to my initial Q to annageek in post #37, it was just because while speaking of LA in general, she only mentioned Lifeline, which afaik doesn't make FLA batteries.
Btw, I'm using "FLA" (for flooded lead acid), rather than "wet LA", because that was my understanding of standard terminology, but I suppose they are synonyms?

I don't really get the idea of multiple 2v cells. The busbars inside the battery connecting the cells, welded on, is always going to be better than cables external to the battery isn't it?
The only reason to separate batteries of cells is weight, ie 50-60kg is about the limit for handling

Good point, but 2V batteries are rather popular in industrial applications, hence my question about "electrical" pros and cons of connecting in series just 2x12V, or 4x6V, or 12x2V batteries to make a 24V bank.
Just think of Trundlebug cherry picker:
as I understand, it needs 300Ah @ 48V, and it's using 24x2V 300Ah batteries.
One alternative, without going into awfully heavy batteries, could be for instance with 2 banks in parallel of 4x12V 150Ah batteries.
According to what you are saying, the latter should be better than the first, but as I said, the multiple 2V solution is popular in many (non-boating) applications... Just wondering why.

if flexi solar panels are availalbe then it gets interesting

+1, also interested to hear more about them, also re. weight, not just flexibility.

 

[James L]

Given this thread is becoming the fountain of battery related knowledge, I have another question for annageek.
Will mixing old and new batteries do much damage to the new batteries. I have 4 115 ah leisure batteries, 2 old ones from when I bought the boat and I added 2 new ones about 2 years ago. The originals are now shot and I will be replacing them. I would prefer to replace just the 2 very old batteries as the others still seem serviceable. Is this a false economy?

 

[James L]

Might be worth waiting another couple of months before buying those solar panels

http://www.extremetech.com/extreme/...boosts-solar-panel-efficiency-by-a-massive-22

not as crazy as the link sounds...

 

[annageek]

Do you include also AGM in the lead acid category?

Yeah, AGM just stands for absorbed glass mat, which is the glass fibre separator that holds all of the battery's electrolyte. SLA, VRLA, AGM are used almost interchangably for marketing purposes. The terms aren't truly equivalent, but close enough for most consumer's requirements.

I've yet to see any flooded Lifeline batteries around...

Nor have I. They're all AGM as far as I know. I was asking if your cherry picker batteries were wets, but if I understand correctly, they're Lifelines, and therefore AGMs.

Regardless, if in your experience there's any cheaper/flooded stuff which you'd recommend, we are all ears!

Again, I can't comment on anything I don't know about. We don't tend to deal much with wet batteries here, and therefore I don't have any real experience with them. Would I go for wets over SLAs? Probably not to be honest. My answer isn't very technical, as I am generalising, but in my opinion, you'll get potentially more cycle life and better reliability from SLAs, providing they are sized perfectly for the application and charged / maintained / looked after properly. As with all these things, spending on the ancillaries to the batteries really is a good way to protect any investment in the batteries.

As for cheaper, well we do deal with some pretty good SLAs that are up at 100Ah, and are cheaper. They're great as general purpose deep cycle batteries, but they simply won't last as long. They're also not great in the slightly more extreme temperatures that can be expected in marine applications. This is where investment into Lifelines really will pay dividends. It's horses for courses with batteries, and without having a really thorough idea of things like the likely usage profile, load profiles, recharge regimes, environmental conditions etc, it's really hard to pick one particular battery.

Firstly, is there any solution which in principle could work better, when combining batteries to create a 24V bank for domestic usage onboard?

Well, from a technical perspective, individual cells (2V) all connected together with a completely balanced set of interconnects, all held in the same place, with an equal air gap between them would be the best solution. But that really is a bit 'spherical chickens in a vacuum', and not overly practical. On large battery arrays, the key to reliability / consistent performance is ensuring all batteries have equal treatment. As the loads go up, this becomes increasing critical. Things to consider are temperature and interconnect impedance.

Interconnect impedance is something that is so frequently overlooked, and even on lowish current systems, it can have a fairly dramatic difference over time. You want each battery to see exactly the same impedance between its terminals and it's load / charger. The most common thing I see is, say 10 batteries all in parallel, with perfectly balanced interconnects between each battery (so far so good!), but then the final connection to the load or charger is taken from the very end battery. This means that the battery at the other end of the parallel array has all the extra impedance of interconnect cabling. It might not seem too significant in your only pulling 25A or so, but you WILL be using the battery closest to the take-off point harder than the others.

Packing batteries together is also a common one. Imaging a 3x3 array of batteries. The middle one is going to get a lot hotter under heavy discharge than the others, and also, the fact that these are massive great lumps of lead, they have quite a bit of thermal capacity. It therefore means that the centre battery has a lower degree of heating and cooling with changes in ambient temperature. They're electrochemical at the end of the day, so heat them up, the chemical reaction occurs quicker and the'll discharge more easily (both into load and by themselves), leading to imbalance.

I think 12V blocks are the way to go. They're more readily available and cheaper than other combinations. The more interconnects you have, the higher the chance of things coming loose / going open circuit etc. The more thermally insulated centre cells of a 12V block can cause problems (as described above), but I think it's a fair compromise for the cost effectiveness of having easier to get hold of, and more heavily developed 12V blocks.

I think on the MegaPulse thing (I'll leave it mostly to Trundlebug), but I expect there will become a time where the battery bank grows so large that the pulse it produces is from a source of such high impedance, it has little to no effect on the battery. God only knows at what point this would be the case, though.

PS: Oh, and one thing I forgot in my previous reply to your post: a very warm welcome to the asylum!

Thank you very much. Been a lurker on ybw since me and my boyfriend started looking and eventually bought our first boat a couple of years ago. I'm well and truly in love with all things boating (even endless posts about boat batteries!) to the point that I'm certain I need a job well and truly in the marine industry. I've learned so much from this forum, and it's great to add my humble opinion to the pot!

I will get around to commenting on the posts beyond #37, but something has cropped up at work and I want it sorted before the weekend!!

 

[MapisM]

I'm well and truly in love with all things boating (even endless posts about boat batteries!)

So, what do we have here, if I understood correctly?
A female engineer, who loves all things boating and cares to answer geeky forumites questions about something she deals with also in her daily job.
In hindsight, this is an event that deserves more than just a warm welcome, I reckon.
A virtual glass of champagne is much more appropriate - with the hope to have the opportunity to share a non-virtual one at sea, one day! :encouragement:

Back to business, many thanks for your explanations.
Both the point on 2V cells with equal air gaps between them and on the effect of interconnect impedance with load taken from one end of a battery array are enlightening - for me, anyway!
Time to rethink my domestic batteries connections, before changing them after installing also the Victron Multiplus this winter!

 

[vas]

I'd also like to thank you for your contribution, ideally it's a thread that should get a better subject line and become a reference for batteries in general as in the four years I've been around I cannot recall another thread having more useful info (now, I said it I guess a few links will be posted shortly enhancing/supplementing the content of this thread )

Interconnect impedance is something that is so frequently overlooked, and even on lowish current systems, it can have a fairly dramatic difference over time. You want each battery to see exactly the same impedance between its terminals and it's load / charger. The most common thing I see is, say 10 batteries all in parallel, with perfectly balanced interconnects between each battery (so far so good!), but then the final connection to the load or charger is taken from the very end battery. This means that the battery at the other end of the parallel array has all the extra impedance of interconnect cabling. It might not seem too significant in your only pulling 25A or so, but you WILL be using the battery closest to the take-off point harder than the others.

so many things that one never thinks of!
If I may, that means that on a 10X1 12V setup you either get the final connection from the mid battery, or even better on a 24V and approx. 400ah system (typically 4X12V pieces) like MM, JFMs, mine and few dozen others in this forum, you're better off getting 4X6V 400Ah batteries in series and be certain that loads are distributed properly Same # of items, same # of potential issues on connections, am I right?

found a few deepcycle solar panel ones for 350usd upwards each, wonder if that would help (sizes are really odd at approx LXWLH:300X190X430mm). I'm asking as my 4X12Vx180Ah ones were similar age but the ones where the current was drawn from were in worse conditioned (and currently scrapped) compared to the "free" end pair. Not really conclusive as I bought the boat s/h but could be a point. Batteries where sealed LA (to my knowledge as this is another issue that needs addressing, how do you differentiate between sealed LA and AGMs? )

looking fwrd to more contributions on this interesting issue.

cheers

V.

PS. then we need a thread on solar panels, I hear the flex ones are carp and I'll be interested to see the first one building b-r patterned ones!

 

[jrudge]

@JFM - so you have 2 port start, 2 stbd start and 4 house?

We have the same and it seemed daft to me 2 starters and 6 house seems the better way to go.

It is tricky to see a downside other than removal of double redundancy which seems OTT.

I don't know how far you have got with this, but I would assume it is only a mild re wire ( and I don't know what spec the engine start batteries are - they are all AGM but I have never looked at them).

Like you battery power is not a huge issue to me, but the more the better and it would reduce gen running times as bit.

It might also allow an inverter to run a few more things - though not as much as a certain new S65 to be delivered shortly!

 

[vas]

May batts are not all in one tray - they are in separate trays 2+2+4 batts (actually GRP boxes with lids and hydrogen vents). So I might as well keep 2x 200Ah for each engine starter (they are monster starter motors; V12 x 32 litre engines). I will measure the domestic batt box this weekend and see what size Lifelines I can squeeze in

thought as much , still would be a nice idea to get the 6 together, even leaving the 2x220Ah ones for starters on both engines.

I have 2 perfect wet LA sealed 220Ah, being the engine starters that have not been busted by dropping to 20v. If only I could get them to Volos you would be welcome to them foc!

The 260Ah are 70kg whereas 220Ah tend to be about 55kg (roughly)

thanks J, very kind of you you've already offered generously more than enough to the MiToS project but I'm probably better off buying them locally unless a freight co does Antibes Athens which I very much doubt (they do London-Athens twice a week though!)

btw, check the values, my cheapo open LA 180Ah ones are around 55kg each, a good quality AGM 220Ah is close to 70kg (ie. unliftable out of dodgy spots, low ceiling trays, I know it quite well...)

I was chatting to another engineer (mech eng) who did his placement many years ago in a local battery factory down here and he explained that since solar panels were introduced a few years ago in a fleet of 20odd rental yachts he was supplying, sales more than halved! Batteries stay charged under the med sun during the summer and topup with no loads during the winter increasing their life (you rarely get proper and longterm shorepower on the hard anyway down here...)

Needless to say I'm designing a smallish h/t for the newly bought 24inch dome and one or two panels but I was told to steer clear of the flex ones

cheers

V.

 

[Siochair]

Has anyone used lead crystal batteries? I've had a look at some of the performance claims and they seem a tad too good to be true.

 

[annageek]

Right... I'm going to have a go at answering some of these Buckle up... this might take some time!

First, as it just popped up:

Has anyone used lead crystal batteries? I've had a look at some of the performance claims and they seem a tad too good to be true.

Yes and yep. We had some in a couple of years ago. They were only smallish (22Ah 12V blocks) and I can't remember the brand. We put them through their paces, and the simply didn't perform as well as a comparable normal AGM lead acid. By my amazing abilities of anticipation (pure chance), I was having a clear out yesterday in the workshop, and found the lead crystal batteries we'd tested. I OCV'd them and they were both down at about 11.8V. Given that we always fully charge before storage, then to go from 100% charge to nothing in two years is horrific! If I remember, I will recharge them next week and high discharge test them and capacity test them just to see how they are now. IIRC, they were pre-production samples, so perhaps they were defective, but I don't know. Either way, I don't expect spectacular results!

Now, JFM's big lithium battery question.

Mixing LiFePO4 (lithium iron phosphate) and lead acid batteries isn't as bad as you might think. The charge voltages are so close, they are compatible. We have actually developed a LiFePO4 automotive battery for motorsport, and, it works find as a lead-acid replacement for alternator charging. We don't recommend charging from lead-acid chargers officially, but the more and more I test this battery and other spin off developments, the more I have become comfortable with charging from standard lead acid chargers.

LiFePO4 charges really well anywhere from about 3.6 - 3.8V / cell. Lead acid charges really well at 2.40 - 2.45V / cell. On a 12V nominal (12.8 for LiFePO4) battery, the lead acid charger is then set up for smack bang in the middle of the ideal charge voltage.

LiFePO4 will also regulate the charge current to near enough 0A when it's full, so in theory, when a charger drops into 'float' mode (typically 13.8ish volts) they just sit there not doing a lot. However, due to natural temperature fluctuations of the ambient temperature, a tiny little charge-discharge cycle happens within the cell. It's an immeasurably small current circulation, but this essentially 'wears out' the battery, reducing the cycle life. Quite how big a deal this is, I just don't know. You can't see it, it just happens, and the only reason I know about it is through reading very long, very boring white papers on the subject. In fact, LiFePO4 chargers tend to be lead acid chargers with a slightly lower voltage and no float charge - they just cut off after stage two of a typical 3-stage charger (absorbtion) is complete.

The nice thing with LiFePO4 is they don't really mind partial charging, and can live happily at low state of charge without any irreversible ill-effect (you do get some mild passivation of the plates, but this clears as you use the battery).

One problem you can get with LiFePO4 is that they don't need a 'head voltage' to charge like lead acid. This means, that if you connect an exhausted LiFePO4 to a full LiFePO4, you can get some pretty meaty circulating current, which can be a bit hazardous, therefore care in application design needs to be taken if you have two separate banks that are connected using a selector switch that will allow you to have either or both batteries 'on line' at any one time. The switch won't like it!

JFM, I agree that the more premium AGM batteries (e.g. Lifelines) would be a good compromise. If I was in your situation, I'd go for the Lifelines. The LiFePO4s are sort of a better option, but as weight is not your main reason for wanting to change chemistry, you're not making the most of the HUUUUGE premium you'll pay. I don't think I could live with that on my conscience, even if I could afford it!

Regards the charging issue and trying to reduce the gen set usage, a solar panel system and decent charge controller would work well towards getting that slow final 10-20% of charge back to your poor, poor, defenceless batteries! I agree with everyone, that it really would help with overall longevity of the batteries, IMO.

There is a potential alternative to using solar to keep check of things. Unfortuantely, for JFM, the load is just too high, and the time between genset use is too short for this to work. Nevertheless, where genset use has to be kept to an absolute minimum and the load is low or the system capacity is really, really, really high, then you can use the genset to get the lead acids up to 80% but also charge a small lithium that is sized to 20% of the lad acidds plus a few hours of load usage. Then, you can use the lithiums to charge (via a DC-DC charger) the slow 20% of the lead acids, as well as take the strain of the load while this is happening, leaving you with perfectly conditioned lead acids, minimal genset use and uninterupted supply. In theory this approach would work for JFM, but the DC-DC charging system would have to work at peaks of up to 100's of amps, and the lithium would have to be about half the capacity of the lead-acid array... so you're probably back to your £20k for just lithiums in a simpler, lighter weight system.

the multiple 2V solution is popular in many (non-boating) applications... Just wondering why.

I am not really sure why either. I feel it may be more down to simplicity, market suitability and practicality than any electrical / technical reason. They are often used for traction batteries too, and you do get some weird and wonderful system voltages involved (e.g. 28V). I guess if you're going to shove that amount of lead at $2000 / tonne into a battery design, you're better off having it in as versatile a package as possible rather than forcing the use of multiples of 6 or 12V.

If I may, that means that on a 10X1 12V setup you either get the final connection from the mid battery, or even better on a 24V and approx. 400ah system (typically 4X12V pieces) like MM, JFMs, mine and few dozen others in this forum, you're better off getting 4X6V 400Ah batteries in series and be certain that loads are distributed properly Same # of items, same # of potential issues on connections, am I right?

On a 10x1 12V array, the best connection would be taken from +VE on battery 1 and -VE on battery 10 (or vice versa), if taken from the middle, battery 5 would be overused and batteries 1 and 10 would be underused. As for the 24V 400Ah array, I think the technical advantages of going for a 4x6V 400Ah array over a 4x12V 200Ah array is negligible, in fact, in this example, I'm not even sure there is an advantage. Therefore, you're better off deciding based on what is available / fits the best / is the most cost effective. For the company I work for, we sell more lifeline GPL-31Ts (12V 100Ah) than any other lifeline battery, and they're often used in multiple battery arrays. I think this is due to the fact that it's the biggest battery that can be easily put into funny shaped holes, and lifted into awkward spots (~30kg).

Incidentally, one thing I didn't mention is if you have for example a 2 series, 4 parallel array of, say 12V 100Ah batteries, you could connect four series strings of two batteries, and parallel across the most positive and most negative points of the series strings. However, you are much better off if you also fit a parallel strap across the mid point of each series string too (think 'ladder' rather than 'box' arrangement). It'll just help keep things in balance.

The lifeline battery technical manual (here: http://www.lifelinebatteries.com/manual.pdf does an awesome job of illustrating what I mean. It also explains loads about other aspects I've spoken about, any a lot applies to any type of sealed lead acid, not just lifeline.

how do you differentiate between sealed LA and AGMs

It's hard to be specific, because some manufacturers call different types of battery the same thing, and some manufacturers call different tyes of batteries the same thing.

Lead acid can refer to: Wet, Flooded, Open, Gel, Straved Electrolyte, AGM (Absorbed Glass Mat), VRLA (Valve Regulated Lead Acid), Non-Spillable, SLA (Sealed Lead Acid), Maintenance Free, and maybe others.

Wet, Flooded and Open cells are all one subset. They have more electrolyte than they need, and can be topped up with deionised water, meaning they can also be accurately measured for absolute state of charge by measuring the specifica gravity with a hygrometer. These batteries are liable to spill acid if inverted, and have to be periodically maintained by adding to the electrolyte.

Gel is a halfway house between open and sealed lead-acids, I believe some are available in sealed, and others in open formats, but having an electrolyte that is a thixotropic gel, rather than liquid means the wont spill.

AGM, VRLA, SLA, Non-Spillable, Starved Electrolyte & Maintenance Free are all generally one and the same thing. You have minimal liquid electrolyte (just enough to allow ion exchange between +Ve and -Ve plates in the cell - i.e., it's starved of electrolyte... sort of). The electrolyte is soaked into a glass fibre mat that keeps the cell's plates apart, and prevents leakage of the liquid electrolyte should the cell's container be cracked. The cell's container is sealed by a bunsen valve. This keeps hydrogen gas inside the cell's container, which then recombines (gas is produced during recharge), so that electrolyte is not lost and maintenance is not needed. The bunsen valve will only operate when there is a positive pressure inside the battery container. This happens during excessive overcharge, and thus regulates the internal pressure to about 4psi to prevent explosive rupture.

Hopefully that summarises how all the terms relate to one another, and why they are all so called. To answer the original question, AGM is sealed lead acid.

Jesus Christ! That was a bit longer than I had expected! Sorry!

All this talk of boat batteries, you'd think I would have some super duper mega hybrid battery system in my boat. Well, I have two batteries. They start the engine. And they're from Halfords! What more do you need! Hehe!

 

[Siochair]

Many thanks annageek :encouragement:

 

[MapisM]

Incidentally, one thing I didn't mention is if you have for example a 2 series, 4 parallel array of, say 12V 100Ah batteries, you could connect four series strings of two batteries, and parallel across the most positive and most negative points of the series strings. However, you are much better off if you also fit a parallel strap across the mid point of each series string too (think 'ladder' rather than 'box' arrangement). It'll just help keep things in balance.

That's exactly what I've got at the moment, if I understand correctly what you mean: 4 pairs of 100Ah/12V batteries, each connected in parallel, total 400Ah/24V.
Or did you mean the other way round? Not that it matters a lot anyway, the following reasoning still stands.

Practically, the type of connection you are suggesting is the one shown if figure 5.3 of the manual you linked, correct?
Well, that figure actually shows only TWO pairs of 12V batteries rather than FOUR, but surely it can be extended with the same logic, I reckon.

I would be very interested to hear what other folks around here with 24V DC onboard have to say about that, because I have a funny feeling that you should explain that also to most boat builders.....

 

[Nick_H]

I have two batteries. They start the engine. And they're from Halfords!

The trucks at your work must have very reliable tailgate locks!

 

[annageek]

That's exactly what I've got at the moment, if I understand correctly what you mean: 4 pairs of 100Ah/12V batteries, each connected in parallel, total 400Ah/24V.
Or did you mean the other way round? Not that it matters a lot anyway, the following reasoning still stands.

Practically, the type of connection you are suggesting is the one shown if figure 5.3 of the manual you linked, correct?
Well, that figure actually shows only TWO pairs of 12V batteries rather than FOUR, but surely it can be extended with the same logic, I reckon.

I would be very interested to hear what other folks around here with 24V DC onboard have to say about that, because I have a funny feeling that you should explain that also to most boat builders.....

I have just re-read my post and realised that saying

However, you are much better off if you also fit a parallel strap across the mid point of each series string too (think 'ladder' rather than 'box' arrangement). It'll just help keep things in balance.

is sort of incorrect (I know what I meant when I was writing it, but explained it all the wrong way around!).

Just go with the lifeline manual illustrations! That shows what I meant all along! And yes, fig. 5-3 is the way to do it. If you ignore the fact that fig. 5-7 or 5-8 show four-terminal batteriestheyit shows the ideal way of linking up larger arrays. That said, in fig. 5-8, if it were me, I would have it such that the final +VE and final -VE connection to the battery pack was taken from opposite ends of the bus bars - not the middle. It'd only make a tiny difference, but with batteries, tiny differences tend to accumulate over time, resulting in big differences!

 

[annageek]

The trucks at your work must have very reliable tailgate locks!

No, it's not that, it's that all of our batteries are fitted with an anti-theft device... that is, a big lead weight that makes it impossible for me to carry them!!!