One battery or two?

[Paragon]

I am looking to install a domestic system of around 220-250ah total capacity and see that there are batteries of around this capacity as well as half this.

Is it better to have two (or more) batteries to make up the total capacity required with some inbuilt redundancy or better to have one big one as it would be more efficient?

Battery type being considered is probably sealed lead acid type, possibly Elecsol, and would be for domestics only!

My thanks for your thoughts in advance

John

 

[bedouin]

It really comes down to practicalities. Most people go for two smaller batteries (110Ah is common) as they tend to be cheaper and easier to handle. A single 220Ah battery is likely to be rather more than you can comfortably handle (typically >50Kg)

Space considerations also play a part - a single large battery probably has a smaller total footprint whereas 2 smaller batteries can be easier to fit in. Many boats have battery storage designed round the standard footprint of the 110Ah battery

 

[Danny]

[ QUOTE ]
...with some inbuilt redundancy...

[/ QUOTE ]As well as Bedouin's excellent advice, your point about redundancy is a valid one - but only if you have an effective battery switching setup. If you just wire them in parallel with no switching or isolation then a major problem (admittedly very unlikely) in one battery might discharge or even damage the other battery.

 

[RestlessL]

Space consideration pushed me down the 2 battery route. I have 2 x 130AH batteries for domestic use.

Rather than have a simple parallel connection, I use a 1-2-both switch so that I can isolate either should I wish - for example to ensure that I have still have a full battery for navigation after a night at anchor. In practice, the switch stays at both for most of the time.

John

 

[Paragon]

Yes this was my thought of operation if the two battery route was followed, but space isn't an issue and whilst I appreciate the weight of the actual battery itself, it will be centrally mounted low down and secured.

I think that the balance seems to be coming down on the side of one big'un as the extra complication of two would appear to not really give much benefit, especially as I have (as a last resort!) a generator on board to recharge if required!

John

 

[William_H]

The primary concern is one of weight in fitting them You don't want to injure yourself in putting them in. Two batteries can be simply paralelled with the option of separating them if you have or suspect you have a problem with one.
I would go for 2 unless one is a lot cheaper and you have lots of help for fitting.
Why so much capacity anyway if you haven't had a domestic system before perhaps 100AH would suffice. olewill

 

[Paragon]

Yes I understand and I'm still torn between the two options! Single battery works out cheaper than two and reason for upgrade is increased demand and desire to be more independent of shore power for longer.

It'll probably end up being whatever I get the best deal on I guess!

 

[bedouin]

What is the increased demand?

One option that may be worth considering is having two separate domestic circuits. One for "essentials" such as nav lights, instruments, VHF and so on and the other for "luxuries" such as fridge, HiFi.

I'm surprised that you find the 220Ah batteries cheaper, in my experience the wide range of "leisure" 110Ah batteries available mean they are cheaper per AH than the bigger ones. My current pair of 110AH batteries cost < £100, but that was 5 years ago.

 

[Paragon]

Additional items are fridge, Eberspacher, TV/video (thru inverter) and usage is more live aboard than occasional.

I was basing pricing on Elecsol 125/270 ah batteries and note that the 125s are £139 and the 270s are £262. Looking at the smaller Elecsol's, you are indeed correct and the 100ah seems substantially cheaper than the 110ah based on Tayna's site!

Perhaps I'm over doing the amp/hr requirement but on the basis that you are only usefully getting a percentage of the battery's quoted ah rating it would appear to make more sense to have more than necessary than "just enough"!

I do see your point about splitting the battery load and am now swinging the other way towards two+ units.

 

[LadyInBed]

"Perhaps I'm over doing the amp/hr requirement "
Is your alternator up to coping with this?

 

[Paragon]

Good question, there are twin 75amp alternators feeding plus a 7.6kva Westerbeke generator if required. I'm hoping that this will be sufficient but welcome any comments if it is felt otherwise!

John