Checking Battery Condition

[Wandering Star]

This is the first of 2 simple questions. The 2 wetcell 120 amp 12 volt batteries that combine to make up my domestic battery bank were replaced less than 2 years ago. They weren't replaced by me and the brand looks cheap! The boat was stored ashore for 12 months without any battery charging or battery useage in that period.

The signs are that my on board charging seems to work fine, with the engine running the batteries charge up but after stopping the engine, the batteries lose their charge within a few hours, seemingly they can go from 13 volts down to 9 volts overnight. (I'm on a swinging mooring so can't use mains power to charge them).

My question is, before I replace them, can I test them to see if they are actually knackered as I suspect they are? There are devices on eBay for around £25 which purport to load test and display the status of the batteries - has anyone experience of these, do they work or are they a waste of money? I'm in Mallorca so "suck it and see" solutions are not easy for non Spanish speaking gits like me. I'd like to be confident the problem is that the present batteries are duds and the solution is to buy 2 new ones and problem solved.

Cheers, Brian.

 

[tinkicker0]

Yes heavy discharge meters are a good test of batteries and a quick look down the throat of a flooded cell type will also show gassing under this test.

From what you say I can be 90% sure that your batteries are boogered, they don't like being discharged for too long.

Why don't you buy a solar cell and charger next time round?

I have a 40w array with a solar charge regulator and in direct sunlight it puts over 2amps in. This will preserve your batteries next time round.

 

[Wandering Star]

Yes heavy discharge meters are a good test of batteries and a quick look down the throat of a flooded cell type will also show gassing under this test.

From what you say I can be 90% sure that your batteries are boogered, they don't like being discharged for too long.

Why don't you buy a solar cell and charger next time round?

I have a 40w array with a solar charge regulator and in direct sunlight it puts over 2amps in. This will preserve your batteries next time round.

Yeah, I suspect you're right. Regards the solar panel suggestion, I bought an 80 watt one last week which I'm shipping out to coincide with my own arrival. Great minds (!) think alike!

Cheers, Brian.

 

[VicS]

The heavy discharge testers are more appropriate for testing a starter battery.

If possible I would get them on a good automatic mains charger, preferably one with a reconditioning facility and try fully charging them.
Failing that a non automatic charger and charge them until you have at least 12.7 volts after an overnight rest.

Then monitor the volts to see how well they retain their charge. A good battery should take several weeks to fall to 12.5 ish

 

[Plevier]

VicS is right - those testers give you little indication of the low rate capacity, just the starting capability.
How thoroughly have you charged them? After 12 months without a charge just engine alternator voltage is not going to wake them up properly unless on for days and maybe not even then (assuming you don't have a smart regulator).
You need a good boost charge - something like 14.5V - for several hours, 12hrs I would suggest under the circumstances but watch they don't get too hot.
Then do a discharge test at something like the 10 hour rate - light bulbs are a convenient load - down to about 10.5V and see what the capacity is like. Then recharge thoroughly again.
You won't get an accurate capacity figure but a good guide.
Don't go down to that low voltage frequently but OK for a test and to wake them up.
If this test doesn't show them to be no good then monitor voltage as VicS suggests.

 

[Wandering Star]

Right, that was all useful advice, I'll get the batteries into a local garage and ask them to fully charge them overnight. Then I'll see how they hold the charge. I'm guessing though, they're duff. I've owned the boat for 6 years but sold her (swapped her actually) for another boat. She went to a chap who was 6'6" tall and he couldn't hack the headroom so sold her back to me early this year. It was in his ownership the batteries were changed and neglected - only pointing this out so I'm not criticized for neglecting my boats!

Thanks a lot.

Cheers, Brian.

 

[William_H]

Battery test

First off you want to separate the 2 batteries and charge and test each one separately. Charge the battery by engine run or charger if possible then disconnect the terminal. heck the voltage next day and if it has dropped to 9v then yes it needs a decent burial. Do the same with the other battery. If both seem to hold their charge with terminal disconnected then you have some drain on the system.
As said next job is to charge them fully both in parallel on the engine then separate them. Connect a 48 watt headlamp globe ie about 4 amps and monitor the voltage. Anything better than half the rated AH is good. Even 25% may suit your needs. A bad battery will drop dead in less than an hour.
I suspect that one or both will prove to be very ill. If only one dead you may choose to persevere with less capacity using only the good one.
Don't forget to also try the batteries at engine starting. They are not specifically made for it but should be able to do the job each individually. If they won't start the engine they are no good to you as an emergency starter battery.
I appreciate your recharging options and capability are limited but even a half charge should I think show good or bad. good luck olewill

 

[tinkicker0]

The heavy discharge testers are more appropriate for testing a starter battery.

If possible I would get them on a good automatic mains charger, preferably one with a reconditioning facility and try fully charging them.
Failing that a non automatic charger and charge them until you have at least 12.7 volts after an overnight rest.

Then monitor the volts to see how well they retain their charge. A good battery should take several weeks to fall to 12.5 ish

Of course.

30 years experience keeping heavy truck wheels turning = not thinking on that they might be dedicated leisure batteries not starter or hybrid types

Still the self discharge rate mentioned likely indicates the possibility of an internal short.

 

[Albert Ross]

Buy a battery hydrometer (under £5). Boring but not difficult to use. I expect you will find your batteries are worn out.

 

[Chris_Robb]

Right, that was all useful advice, I'll get the batteries into a local garage and ask them to fully charge them overnight. Then I'll see how they hold the charge. I'm guessing though, they're duff. I've owned the boat for 6 years but sold her (swapped her actually) for another boat. She went to a chap who was 6'6" tall and he couldn't hack the headroom so sold her back to me early this year. It was in his ownership the batteries were changed and neglected - only pointing this out so I'm not criticized for neglecting my boats!

Thanks a lot.

Cheers, Brian.

You mention that the batteries dropped from 13V to 9V. What was the voltage whilst the engine was running? Was it only 13V or was it nearer 14.4V? I say this, because you may in addition to duff batteries, have a charging problem with the alternator. If anything below 14V you have a charge problem, which can be caused by a number of factors, bad wiring, bad connections, splitting diodes, etc, (but probably not and alternator problem)

 

[rob2]

There are more complex drop testers, but you're unlikely to find one on ebay. A friend tested my batteries and before the test he programmed the details of the battery type and size into the tester. The result gave condition and estimated capacity. Mind you, he used to work for Lucas, so I guess this was the dog's goolies of testers!

Rob.