Two leisure batteries instead of one leisure + one cranking?

If you have 110 AH battery it is really quite big. Even though not designed to do so it should start a small engine with ease.
The point about a cranking battery is that it will provide a lot of amps in a small light weight package for cars. A battery designed for storage will not give a good current and may be damaged by cranking but that is really in relation to its size. (usually huge). ie a big storage battery will easily supply as much current as a tiny cranking battery.
So yes to the original poster the battery set up is OK especially if you mostly start on both batteries.
However don't forget to occasionally test start on each battery alone to ensure it will do so. And of course only use on alone for services so if it is discharged you have a good one to start engine.

good luck olewill
 
How flat is "completely flattened"? If you've got a cutoff to disconnect at not less than about 10.5V (for a 12V battery) running down to it occasionally won't matter as long as it's recharged soon. Going lower than that or doing it repeatedly, and worst of all leaving it in that discharged state for some time, especially in warm weather - bad news. If they have literally been flattened to 0V you might have trouble getting them to charge again at all.

"Leisure" battery has no specific meaning. However in general they would have thicker plates than car size cranking batteries, and extra separators. The plates would be (similar to) truck battery plates. They aren't intended for such heavy currents in relation to their size as car cranking batteries, but when you think of (e.g.) a high compression 2 litre diesel in a car starting from maybe a 50Ah battery, a small yacht auxiliary engine is unlikely to worry a 110Ah leisure battery. If you were selecting a crankng battery for the job, it would be a lot smaller than 110Ah wouldn't it? Don't try starting your Sunseeker with the leisure batteries though!

You could do a capacity test. Put on enough lights for about 10A load and see if it takes around 10 hours to go down to around 10.5V. It's all very approximate (and temperature dependent) and capacity will start to reduce early in life so don't expect 100% unless they are new. Don't expect to get 5 hours if you put 20A on; the higher the current the lower the deliverable capacity.

Mike
 
Bob

I too am in Devon and find this forum invaluable for advice.

I bought a boat a couple of seasons ago that had two 110 Ah batteries, one of which was used for engine starting. This winter I am having to replace them as one in particular no longer holds its charge. At the same time I am installing a third battery to start the 20hp diesel fitted. This will not only create a dedicated engine battery but will have two x 110 Ah domestic batteries which should last longer betweeen charges. I will of course ensure they do not discharge too far.

To help with the extra charging I am also installing a Sterling Alternator to Battery charger which charges the engine battery first then automatically switches over to the domestic batteries. I am hoping that this bit of kit will take a lot of the worry away as to whether everything is charging correctly - we'll see.

From my experience with the two battery set up I would not let it be a deal breaker just because of the batteries although if they are currently flat they will undoubtedly be damaged in some way and will need replacing sooner
 
[ QUOTE ]
If you have 110 AH battery it is really quite big. Even though not designed to do so it should start a small engine with ease.
The point about a cranking battery is that it will provide a lot of amps in a small light weight package for cars. A battery designed for storage will not give a good current and may be damaged by cranking but that is really in relation to its size. (usually huge). ie a big storage battery will easily supply as much current as a tiny cranking battery.
So yes to the original poster the battery set up is OK especially if you mostly start on both batteries.
However don't forget to occasionally test start on each battery alone to ensure it will do so. And of course only use on alone for services so if it is discharged you have a good one to start engine.

good luck olewill

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Sorry William - but cannot agree there. AH size of a battery makes no odds to current it can deliver, it only alters the length of time it can deliver.
A soft plate battery as most true leisure batterys are cannot deliver the amps required to start a battery and if they try - the plates buckle - no matter how big the battery.

If as amulet says - system on board does the job, then no real reason to change. My personal view after having ruined leisure batterys, survived with various ... is good size car / truck battery for starting and a good size compromise leisure battery for domestic / back up to starter battery. And yes I am like amulet a keen supporter of the old standard 1-Both-2-off switch.

Big batterys don't always make big amps !!
 
A subject on which most people have deep convictions hence the number of posts. I see no great problem with your set up it is not ideal but life is one big compromise anyway - just get a reduction in the purchase price becuase they have been flattened.

For whats its worth I only use and buy cheap £60 van starting batteries 108a these last 5-7 years on a two battery system. Yacht is 21 years old has Ford 4 cylinder engne and 2 fridges so overnight sailing puts a fair drain on the system - have never run out of juice. Always keep the newest battery for final use and start the engine and run all circuits on the oldest and thus the weakest of the two.
 
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AH size of a battery makes no odds to current it can deliver, it only alters the length of time it can deliver.

Mmm. Isn't that a bit oversimplistic? Neither this poster nor I in a very similar simultaneous post were suggesting a bigger battery would automatically give more. Different design optimisation will give a different cranking capability per Ah of low rate capacity, or per unit of plate weight, which is virtually the same thing, but within a design, cranking current and Ah will go hand in hand.

A soft plate battery

I don't recognise that term (after working for a major manufacturer for 10 years, admittedly a while ago), can you explain it please?

as most true leisure batterys

also that term, I'm not aware of any standard for "leisure" batteries unless there is a very recent one?

Mike


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I do think it's a pity batteries aren't all labelled with both CCA and AH ratings which would make it much easier to compare different ones and to know what you are getting. Most leisure batteries are advertised as also suitable for starting yet the fact their CCA ampage isn't quoted clearly shows that engine starting is not considered their prime function.
 
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