Old Engine Battery as new House Battery?

oilybilge

oilybilge

Well-Known Member
Joined
3 Nov 2017
Messages
213
Location
Suffolk
Visit site
Afternoon all. My 24-footer has two 110ah leisure batteries. The engine battery is in rude health, but it looks like the house battery is on its last legs. Would it be okay to redeploy the engine battery as a new house battery (and buy a smaller battery for the engine)? Or would years of doing nothing but cranking the engine mean that it can't do anything else now? I suspect it'd be okay but I wanted to check -- this is all so much alchemy to me. Cheers!
 
If it's one of the batteries that's gone gammy the other is probably not far behind if they were bought together. Batteries are disposable items with a limited life.
 
Last edited:
Yes - I did that. You don't really need 110 Ah for engine starting - you need CCA (cold cranking amps). Saved some space in the locker.
 
Yes to a smaller start battery. You can go as low and cheap as a basic 50ah or so for a small diesel car like a Citroen - just make sure you only use it for the engine.. then try your existing battery for the house but recognise that it is also probably getting near the end of its life. Then your choice is a so called leisure battery but now for very little more you can get an AGM of similar capacity which in all respects is better value long term.
 
C'mon.

Do the right thing and disconnect both batteries, then fully charge them individually and measure the voltage. Leave them for 24 hours, re check the voltage to know how much they drop when not connected. Then load test them.

image.jpg


Replace any that is not ok with a new, specifically designed for each use (start / domestic). Get the biggest you can fit/afford, meeting or exceeding the engine manufacturer's requirement for start battery..
 
Last edited:
ChromeDome said:
C'mon.

Do the right thing and disconnect both batteries, then fully charge them individually and measure the voltage. Leave them for 24 hours, re check the voltage to know how much they drop when not connected. Then load test them.

Get the biggest you can fit/afford, meeting or exceeding the engine manufacturer's requirement for start battery..
Click to expand...

Agree with the first bit.

However, very few manufacturers are specific about size or type of start battery although some will quote a minimum CCA A "large" battery as in in notional Ah capacity is simply not needed. The OP has a 26' yacht and the engine is likely in the 10-20hp range. These are really simple low specific output engines and a car battery for a 1 -1 1/5 litre engine is more than enough. I used a 45Ah for a small Citroen for my 14hp Nanni. For my new Beta 30 I have a 28Ah Odyssey AGM as used in competition cars. My Morgan has a similar Red Flash, still going after 19 years. Downside of these high current batteries is cost but the pros are small size, can be mounted in any orientation and very long life.

The use of dual purpose large capacity batteries for both start and house date from the days when boats were wired to use both or either batteries for both or either purposes. Things have moved on and it is now easy to split the banks completely and use dedicated batteries for each bank and the requirements for start batteries are very different from house.
 
AngusMcDoon said:
If it's one of the batteries that's gone gammy the other is probably not far behind if they were bought together. Batteries are disposable items with a limited life.
Click to expand...

Not necessarily so. Engine batteries are usually depleted very little each cycle, and quickly fully recharged immediately afterwards. That's what they like, and which leads to a long life. By contrast a boat's domestic battery is much more likely to be often severely depleted, and may well not be fully recharged for some time. That leads to premature failure.

I am in the 'Yes, redeploy the old engine battery for domestic use, and buy a smaller engine battery' camp. The worst that can happen is the domestic battery will need replacing soon, too, in which case the OP has lost nothing over splashing out now, but it probably won't need replacing for some time yet.
 
Batteries can be designed for 2 very different jobs. To start an engine with high current or to provide low current for long period. Yes you can buy a "leisure" battery designed to do both jobs but for service ie low current low period they are not as good as a "Deep Cycle" battery. (OK but a compromise)
The fact that you quote Amp Hour capacity of the battery currently used for the engine implies it has some deep cycle capability. So yes give it a try as house battery.
For engine start CCA cold cranking amps is usually quoted as a measure of the size of the battery. These type are likely to be cheaper and more avaialble because it is what a car uses. Great for engine start not so good for low current long period discharge. Try not to do that to it. However your house battery though not designed for engine start can probably provide a lot of current for engine start in an emergency. (jump start). ol'will
 
Can we just check that the OP has a charging/switching that can isolate the engine battery after a decent recharge period ? Sounds as if it has, but it's worth making sure.
 
Thanks for the replies chaps. Very helpful.

Regarding the age of the batteries, I know that one is from 2013 and one from 2015 but I don't know which is which. I only bought the boat in 2017.

It originally had a 1-2-both-off switch which I replaced with a Blue Seas ACR.

The engine is a Beta 20.

So yes, I think I'll go ahead as planned -- new starter battery, and use old 110ah engine battery as new house battery and see how long it lasts.

Cheers!
 
You must log in or register to reply here.

Other threads that may be of interest

N
Lithium battery fire
2 3
Replies
50
Views
2K
lustyd
lustyd

Share this page

Top