Testing batteries?

[Allan]

The new boat has 3 batteries they are all the same type, leisure batteries and the same age. Two are linked with large copper links and are used as domestics the third one is a start battery. If all 3 are OK I would like to link them all together, to increase the domestic bank and then add a dedicated start battery.
My first question is, what is the best way to test each of the three batteries.
Secondly, the engine is a Volvo penta 2030, what is the best start battery?
Allan

 

[VicS]

A good quality car battery of the recommended size ( 70Ah ???) will be adequate

A Red Flash High rate battery better esp if you are looking for a compact AGM battery that can be even used on its side But take care in the choice because Red Flash quote maximum discharge current which suppliers seem to trasnlate into CCA. You need to check the true CCA figures and get one equivalnet to a car type 70Ah one (I'd think a Red flash 1200 would do the trick, maybe even 1100)


Optima Red top claim to be the ultimate starter batteries but are less expensive than the Red Flashes


As for testing the existing batteries. I would charge them fully and independently with a good multi stage charger.
then monitor their open circuit volts while standing with no further charging and no load for a period of a couple of weeks or so .

If they have filler caps also test the electrolyte density.

"Drop test" perhaps but not so relevant for a domestic battery as it is for a starter battery

 

[William_H]

I would go ahead with fitting you new starter battery. Then as Vic says make sure all batteries are fully charged. Then use then one at a time isolated from one another. Put a load on be it a fridge or lights TV etc and just see how long it takes each battery to drop to a figure like 11.8v. You may be able to work out the amp hours taken from each battery. If you get about 20 or 30 amp hours out of each one you will be doing well. ie about 50% of claimed AH rating. If any one battery is cream crackered you will soon know. If they all perform about the same then it will be safe to parallel them for charge and discharge. But beware any time you have any doubts about the house battery performance isolate them and check individually. Essentially if they don't do the job you want then they are no good. good luck olewill

 

[lw395]

Like Olewill, I would charge them fully, then put a load of perhaps 10A on each for an hour or two, see that they all end up at a reasonable voltage, and a similar voltage.
I would not worry too much about a reasonable amount of self discharge unless you intend to leave them standing for long periods.

Alternatively, I might consider keeping one of the house batteries separate for the fridge or other big load. Depends on your particular electrical use I think?

 

[DuncanHall]

Allan I had a similar problem a year or so ago. To test the batteries I used a constant load and monitored the voltage drop over time until it dropped to about 11.5 V. I used a old car headlight as a load that resulted in a 5A current.
I have 3 batteries for the domestic as you propose. Its better to keep them together as the effective capacity is greater combined rather than separate.

I use a redstart battery to start the engine but thats due to space limitations. That said its 6 years old and still going strong. It outlasted the domestic bank.

Duncan