Service Battery Bank - 1 or 2 batteries?

[Paragon]

Traditionally I have always had an engine start battery and two or more individual batteries in parallel to provide the service bank.

As I am about to renew the service bank and space is limited, other than redundancy, is there any other reason why two 110ah batteries in parallel are better than one 220Ah one?

This would be for the service bank only, engine and thruster are on their own batteries!

Thanks in advance

 

[sailorman]

Traditionally I have always had an engine start battery and two or more individual batteries in parallel to provide the service bank.

As I am about to renew the service bank and space is limited, other than redundancy, is there any other reason why two 110ah batteries in parallel are better than one 220Ah one?

This would be for the service bank only, engine and thruster are on their own batteries!

Thanks in advance

is there any other reason why two 110ah batteries in parallel are better than one 220Ah one?


easier to handle for starters ( pun )

 

[pvb]

As I am about to renew the service bank and space is limited, other than redundancy, is there any other reason why two 110ah batteries in parallel are better than one 220Ah one?

Not really. As sailorman has said, the weight issue of a 220Ah battery can be a factor in deciding. It's also usually the case that a single 220Ah battery is cheaper than two 110Ah batteries.

 

[pappaecho]

Definitely. My 2 house batteries were bought 4 years ago at the same time. One had a bad cell last year and was replaced. Other is fine. So half my investment is still working.

If I had fitted a 220 a/h/ single battery it would be totally u/s

 

[Trundlebug]

Two 110Ah better than one 220Ah.

Batteries last longer and have more capacity if the speed of discharge, i.e. discharge current is less.

With one battery, if you withdraw say 4 amps, with two batteries in parallel you're only withdrawing 2A from each. So ultimately you'll get more capacity, and they'll last longer.

Probably not a huge difference, but combined with the factors mentioned above, i.e. easier handling and redundancy in case of cell failure, as well as the fact that 110Ah batteries are much easier to get hold of (better availability) it adds up to a better package. IMHO anyway.

110Ah batteries were available for as little as £65 each this season. Can you get a 220Ah for £130?

 

[noelex]

Two 110Ah better than one 220Ah.

Batteries last longer and have more capacity if the speed of discharge, i.e. discharge current is less.

With one battery, if you withdraw say 4 amps, with two batteries in parallel you're only withdrawing 2A from each. So ultimately you'll get more capacity, and they'll last longer.

Probably not a huge difference, but combined with the factors mentioned above, i.e. easier handling and redundancy in case of cell failure, as well as the fact that 110Ah batteries are much easier to get hold of (better availability) it adds up to a better package. IMHO anyway.

110Ah batteries were available for as little as £65 each this season. Can you get a 220Ah for £130?

2x 110 AHr and 1X 220AHr will have the same capacity

 

[Frayed Knot]

Have you considered twin 6volt (Trojans) wired in series?

I went this way a couple of years ago & would certainly do the same again if I ever change my boat. More far usable amps & no worries about plate-damage even if they're completely drained. Only drawback I know of is that they probably wouldn't crank the engine in an emergency.

 

[Paragon]

110Ah batteries were available for as little as £65 each this season. Can you get a 220Ah for £130?[/QUOTE]

No - but I've seen one for £160!

Still I take the points about handling, the 110ah tend to be 25-28kgs whereas the 220ah is around 50kg but physically one fits easier than two.

Ok, so apart from redundancy and ease of handling, it appears there is no real difference or specific reason to have two.

 

[Trundlebug]

2x 110 AHr and 1X 220AHr will have the same capacity

Only nominally.

Capacity varies with rate of discharge, ref my post above.

Discharging faster reduces the capacity.
The nominal capacity is quoted for a fixed discharge rate. If you discharge faster than this, the capacity will be reduced, and vice-versa.

 

[pvb]

Only nominally.

Capacity varies with rate of discharge, ref my post above.

Discharging faster reduces the capacity.
The nominal capacity is quoted for a fixed discharge rate. If you discharge faster than this, the capacity will be reduced, and vice-versa.

I think you've misunderstood this. Nominal Ah capacity is usually quoted at the 20 hour rate. Certainly, discharging faster than this reduces the effective capacity. However, the degree of faster discharge is measured relative to the 20hr rate, and the 20hr rate of a 220Ah battery is double that of a 110Ah battery. Therefore, to all intents and purposes, drawing 4A from a 220Ah battery (your example) is exactly the same as drawing 4A from two 110Ah batteries in parallel.

 

[noelex]

Only nominally.

Capacity varies with rate of discharge, ref my post above.

Discharging faster reduces the capacity.
The nominal capacity is quoted for a fixed discharge rate. If you discharge faster than this, the capacity will be reduced, and vice-versa.

PVB has explained it better than I can can.

Peukert's Formula is dependent not only on the discharge rate, but the battery size..

So 2A out of a 110AHr battery is the same as 4A out of a 220AHr battery.

The battery capacity of 2X110 AHr batteries is the same as 1X220Ahr battery regardless of discharge rate.

(assuming the batteries are identical otherwise and ignoring the very minor loss in interconnecting cables etc)

 

[maby]

As others have said, there is no fundamental difference and having two lower capacity batteries in parallel does give you some theoretical protection against a failed battery, but only if the circuit is designed properly.

Our brand new boat, straight from the factory, has two domestic batteries, but they are hard-wired in parallel which rather defeats the redundancy associated with having the two. If either of them starts to deteriorate, it will drag down the other. One of these days I'll get round to fitting a proper isolator switch to allow me to disconnect either battery if it fails....

 

[Chris_Robb]

Two 110Ah better than one 220Ah.

Batteries last longer and have more capacity if the speed of discharge, i.e. discharge current is less.

With one battery, if you withdraw say 4 amps, with two batteries in parallel you're only withdrawing 2A from each. So ultimately you'll get more capacity, and they'll last longer.

Probably not a huge difference, but combined with the factors mentioned above, i.e. easier handling and redundancy in case of cell failure, as well as the fact that 110Ah batteries are much easier to get hold of (better availability) it adds up to a better package. IMHO anyway.

110Ah batteries were available for as little as £65 each this season. Can you get a 220Ah for £130?

Another factor is that it may be easier to mount 2, or even 3 110AH batteries than 1 x 220 AH.

I would also issue a warning on those buying the very cheap lead acid, and charging heavily with Sterling chargers at 14.8V (- which does in fact give VERY fast charging). I have destroyed 4 x Numas 110AH in less than a year. They all gave up the ghost in a variety of ways, 1 overheated and filled the cabin with sulphuric acid - had to be dumped over board - truly frightening. The next just fizzed on float volts (13.5) and the others ( i was down to 2) lost so much charge over night compared with the usage, they were in fact knackered. Each one when inspected by the supplier had loose positive poles, I suppose because they were just not of sufficient quality to take such a high charging rate.

I now have a set of sealed (Re-converting type) batteries and charge at 14.4V.

The first thing I noticed is that charge amp rates are down at start up from 85amps to about 55 amps, and trhat the over night drop in voltage is only very marginal - ie usually no less than 12.5V in the morning even with load from the fridge. The old ones were dropping to 12.1V overnight on using 30 amps from a bank of 440AH.

Sterling is now saying that you can't use his chargers on cheap lead acid - they are just not robust enough. Shame he advised it in the first place!

 

[noelex]

Our brand new boat, straight from the factory, has two domestic batteries, but they are hard-wired in parallel which rather defeats the redundancy associated with having the two.

My boat is wired with 2 separate house banks (and a separate start battery). I think this has a lot of advantages for a cruising boat.

2 hard wired parallel batteries do still provide some redundancy however. If batteries die a gradual death as many do, usually all the batteries will be similar, but sometimes a shorted cell will result in a sudden drop in battery performance.
This latter condition is where removing the defective battery from the bank can reveal a still useful life left in the remaining batteries.
When this sudden drop in battery performance occurs and it is easy to test the batteries and remove the defective one from the system, even if these are hard wired.
If the batteries have experienced a gradual slow death there is usually little point in isolating one battery as the other batteries in the bank will be in a similar condition. Although it can sometimes provide some battery power while replacments are orginized.