Battery capacity

[saltyrob]

Hi Folks,
We have a 28 foot yacht fitted with two batteries. Unfortunatley the domestic battery appears to have died, therefore will be replacing with two new batteries.The existing engine starting battery is 110 ah and domestic 105 ah.I have been offered a good deal on two 100 ah batteries and would like advice on whether they will be adequate.Our boat is fitted with standard navigation lights,gps, radio and a fridge which we keep on only when the engine is running.
Existing and proposed batteries are dual purpose.
Many thanks

Rob

 

[FullCircle]

Should be Ok. Pay aobut 60 quid each for 100Ah leisure batteries.

 

[Dave_Seager]

Why replace both batteries if only one has failed?

 

[jeremyshaw]

Not sure what you mean by "dual purpose". Generally crankers and house batteries have quite different requirements. 100ah seems a bit big for me as a cranker - I was happily cranking with 80ah for a 40hp engine. I would be inclined to get the right sized cranker and a bigger house battery for the same money.

 

[MarkJohnson12345]

Agree that 100 a/h is big for a starting battery.

We use an 85a/h, which again is well sized.

But before you go too far down the scale, just think that sometimes in the winter, you might have to turn the engine over quite a lot to get it started.

Nice to have a few amps extra in that case. Also if the domestic gets a hammering you do have an hour or two with the starting battery if you are brave!

 

[tobble]

I think he means he's going to replace the one dead domestic with a bank of two, and not do anything to the starter.

my guess is that will be fine but depends a little on your charging systems. Assuming you sail every few weeks, the engine alternator plus somehting to gradually replenish/maintain between trips, in the way of a small wind gen or PV panel would be ideal.

not sure about the dual purpose coment though; as already alluded to there are 'cranking' batteries which have spongey plates (lots of surface area = high current) or deep cycle batteries with solid chunky plates (more robust). so called 'leisure batteris are a compromise between the two. I'd be inclied to go for a deep cycle if you have segregated banks - in practice a largeish bank of deep cycle will have not probs starting your engine in an emergency. the deep cycles will last a lot longer.

I'm sure there are people wh disagree...

 

[saltyrob]

Hi,

Just to clarify, the boat is fitted with two batteries one for the engine and other domestic They are same type of batteries although with lightly different ah. Have been adviced that its always a good idea to replace both batteries as weaker one can pull the voltage in the other down.Both existing batteries have heavy duty 664 printed on them and have down at least 6 seasons

Rob

 

[mikehibb]

Makes my boat sound a bit inadequate in the battery capacity.

33ft with yanmar 3gm, chartplotter, vhf, fridge etc.
Only have 2 55 Ah batteries, one for engine and one for domestics.
I only do day cruising at the moment but never had a problem. They were going to be the first things that I was going to upgrade.

Engine starts well on the 55 Ah, then cools the fridge down pretty quickly whilst both batteries are charging also whilst heating up a tank of water via the calorifier.

I warm up the engine before heading out, usually takes half an hour to get out of the marina and sails up from engine start time. run the engine again for the anchor windlass when anchoring up for lunch, this gives a little extra to the fridge and calorifier. Beer is still cold at end of day. Not found out how much the autopilot will suck out of the battery yet, as we only day cruise and we enjoy taking the helm rather than letting Larry (for that is its name) do it.
Engine started first time last month after 2 months sat without any charging.
Not even sure of the age of the batteries, are the same ones that were on when w got the boat nearly two years ago.

ps now I have posted this, I bet fate has been tempted...

 

[nickcred]

lol i think I am overpowered the, 25ft Birchwood with fridge, nav lights and 5 strip lights, have 2 x 110 ah domestic and 1 x 85 ah starter and we are still paranoid about using the lights and fridge on battery, am i panicking for nada

/forums/images/graemlins/laugh.gif