Mixing batteries

[mireland]

Is it wise to mix a Red Flash 1000 starter battery (AGM) with cheapo lead acid leaisure batteries for the domestic stuff. They will be used with an Adverc regulator thingy and a 1, 2, both or off switch. At present no splitter diode or relay etc.



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[pappaecho]

I would suggest that for domestic you need deep cycle battery(s) not cheapo lead acid stuff - eg car batteries. I can buy a 100 amp hour deep cycle battery at my local chandler for £60.
Car batteries provide high output in terms of amps for a short period. Deep cycle batteries provide a regular output over many hours.
I have never needed splitter diodes, and usually charge both batteries either from a solar panel or in the "all" position when the engine is running

<hr width=100% size=1>Def: Yachting - a way of spending the kids inheritance

 

[mireland]

Does this mean you do not use a separate starter battery? There seem to be plenty of deep cycle batteries around at that sort of price but I had read that a dedicated gel battery for starting was worth the little extra. The Red Flash jobby retails at about £80.

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[charles_reed]

Re: Mixed batteries

Seems a curiously obsessional and conspicuously wasteful thing to do, though conventional wisdom, to use one battery for only starting the engine.

I rotate my 3 of my 4 batteries for that purpose (1 is always domestic).

You definitely need a splitting diode, especially with the Adverc, or you'll find out shortly the risks of having one fully-charged battery being suddenly put into circuit with fully discharged ones.

Don't forget the splitter gives about a 5% voltage drop.

The solar panel(s) and wind generator in my set-up feed straight into the main circuit bus so will only charge those batteries which are in use.

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[reeac]

There is a school of thought that believes that you if your battery storage space is limited than it's better to have all or both batteries of the deep cycle type. That way you will have more useful capacity although you'll have to be careful to retain enough charge in one of them in order to start the engine. I've certainly followed this practice for several years with no problems.

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[pvb]

Bad value...

Red Flash batteries are more expensive than ordinary batteries, and are primarily bought because of their size/weight advantages. If you've got a Reinke Super 10, I wouldn't have thought that size or weight were major concerns in choosing a starter battery, so I'd spend the money instead on a larger capacity conventional lead-acid battery.



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[Anonymous]

Re: Mixed batteries

>>Seems a curiously obsessional and conspicuously wasteful thing to do, though conventional wisdom, to use one battery for only starting the engine.<<

Most deep-cycle (often called 'leisure' batteries are not designed to provide the sort of current needed by a cold engine starter - or bowthrusters and anchor windlasses, come to that. If your domestic battery bank is large enough - many hundreds of Ahr - by putting several batteries in parallel, then you will possibly find you have enough CCA (Cold Cranking Amps) available.

The other problem with not having a dedicated cranking battery is that you might come back to the boat to find that someone had left a load on without your knowledge and you haven't got enough power to start the engine. If you have a generator than maybe that's not a problem (anyway, you could jump-start the main engine from the generator battery if you wanted).

I am now going away from a seperate cranking battery in favour of 5 135Ahr batteries all in parallel - I have a 6kVA generator and an 80A mains charger and I am fitting a copious solar array as well. However, I am fitting an isolator switch on the battery box so that I could 'ring-fence' one battery for cranking, in the event of the generator failing.

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[charles_reed]

Cranking batteries

Most sailboat engines have about a 2.5kW starter motor, well within even the most lazy Pb/Ca battery, to provide sufficient cranking current.

In fact you'll find an increasing number of diesel cars being fitted with what are effectively deep-cycle batteries.

The theory was possibly valid 20 years ago, when battery manufacture was pretty hit and miss.

What is probably more valid is the siting of the cranking battery - to prevent voltage drop you need a run of less than about 1.2m in 25mm2 cable - and boat domestic batteries are frequently sited more than that away from the starter.

In reading my post, I note I didn't answer the question about mixing deep-cycle and cheap lead-acid batteries.

The answer is, of course, it's inadvisable - Pb/Ca batteries require a higher charge voltage, and are slower to accept charge than lead/acid.

In practice, providing the Pb/Ca battery isn't being used for the heat sensor of a smart voltage regulator it seems to work.

I'm not referring to the lead-acid so-called "leisure batteries", frequently sold at an inflated price. All they need apparently is a longer period of taper or equalising charge.

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[Anonymous]

Re: Cranking batteries

I have spent much of the last few weeks researching batteries and am starting to get some reliable information (i.e. ex-reputable mfr not old wives' tales).

According to Exide and Varta (and other reputable manufacturers) the deep-cycle leisure batteries should NOT be used for cranking. High currents weaken the plates and shorten life, as does fast charging

:-( Don't have actual numbers on the latter, yet, am still researching as it is a real issue for most of us, as is use of bowthrusters and windlasses.

>>.... Pb/Ca batteries require a higher charge voltage, and are slower to accept charge than lead/acid...In practice, providing the Pb/Ca battery isn't being used for the heat sensor of a smart voltage regulator it seems to work.<<

Let's put this chestnut to bed. Traditionally antimony was used with lead but the problem with that is that it results in high water usage. Nowadays they use cadmium instead of lead which results in nearly maintenance-free batteries even of the flooded open sort. Ever wondered why you don't need to top up as often these days? That's because everyone uses Pb/Cd. I'm not sure that anyone still uses lead antimony. Aside from that the voltages are the same and the charge characteristics are the same - at least it is for all practical purposes, they say, no doubt there are minor differences.

>>I'm not referring to the lead-acid so-called "leisure batteries", frequently sold at an inflated price. All they need apparently is a longer period of taper or equalising charge.<<

Not so, at least not from the reputable suppliers. God knows what the badged batteries are - and the market is flooded with them so BEWARE - but reputable manufacturers supply batteries of a different plate design for deep discharge (i.e. leisure) to compared to automotive (commercial or whatever).

Some names we can trust in the UK:- Yuasa (bought the old Lucas factory) and make under a number of brands. Exide. Varta. Sonnenschien. I would give a list of those batteries that have failed my simple vendor assessment but I fear legal consequences, so sorry, no can do. But caveat emptor - there is big money in batteries, there are many cheap imports and there are plenty of cowboys.

As for answering the question about mixing batteries in parallel....never mix batteries of different sizes, manufacturers or even vintages from the same manufacturer together. One battery is always the strongest and takes most of the load.


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[Anonymous]

Re: Cranking batteries

Erratum:- In my post I said "Nowadays they use cadmium instead of lead...." which should, of course, have read "Nowadays they use cadmium instead of antimony....." I think that was fairly obvious from the context but I apologise for any confusion.

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[andy_wilson]

Nah.

Get a whopping great truck battery designed for starting and tail lift operation. 140 Ah for around £70 from a truck factors.

When your other battery needs replacing, get another identical one.

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[Joe_Cole]

Re: Mixed batteries

FWIW I have always been under the impression that a "Leisure Battery" is not a true "Deep Cycle Battery". I think that they are a half-way house between a cranking battery and the true Deep cycle ones.

Having said that I use Leisure batteries, though I take care to ensure that they are not heavily discharged. My last one lasted 5 seasons and was only replaced because its capacity had dropped a bit. A 75AH replacement cost around £27.



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[Anonymous]

Re: Mixed batteries

>>I have always been under the impression that a "Leisure Battery" is not a true "Deep Cycle Battery". I think that they are a half-way house between a cranking battery and the true Deep cycle ones.<<

The well known brands all use the term 'leisure battery' and describe them as being suitable for 'deep cycling' which seems to mean 50% on a regular basis, or, with a sacrifice of some life, 80%. The only manufacturers who have told me that they can go to 80% are Sonnenschein (gels, v. expensive) but their published literature shows that the life is reduced very considerably.

>>Having said that I use Leisure batteries, though I take care to ensure that they are not heavily discharged.<<

That's the 'correct' thing to do. Not necessarily the cheapest, but it is correct and if you want a trouble-free life that's the way to go. The issue now is whether your engine start, bowthruster and windlass currents are excessive for that battery and whether any fast charger is too fast for them. In your case you already know the answer - if you are getting five years, you can't complain!


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