Battery Tester - recommendations please

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peter2407

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I am looking for a battery tester to test whether a battery is worth charging or whether it is FUBAR. Would appreciate any recommendations.
 
 
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These testers will only verify starting capability.
No use for checking domestic batteries.
(Nigel will disagree.)

As an example, recently I ran a tyre inflator - about 8 amps - from my wife's car battery, which I thought was in OK condition. After 10 mins - just over 1Ah from a 40Ah battery - it slowed down a little bit.
Wife waiting to go out - tried to start car - wouldn't turn over at all.
Gave it 10mins charge and car started.
When she came back in after maybe 30 mins running, tried it with a 100A discharge tester for 10 secs - passed with flying colours.
Put headlights on for a few minutes - dead.
Ordered new battery.
 
Troubadour said:
These testers will only verify starting capability.
No use for checking domestic batteries.
(Nigel will disagree.).
Click to expand...

I think they can be useful tools, but I agree they have limitations. In your example, I would have allowed 24H after charging, and would ideally have a second battery to compare the results with.

I used one similar to the Silverline model to identify the faulty domestic battery in a bank of three, removing it doubled our capacity.
 
sailinglegend420 said:
It is NOT designed for testing the Ah capacity of deep cycle batteries.
Click to expand...

That is not what the OP asked for.

Testing the capacity of batteries requires a very expensive bit of kit, nobody is suggesting that these devices can do the same job. They are useful for putting the battery under a fairly heavy and calibrated load, and testing the voltage. As such, they can detect a battery that is end of life, especially if compared with another.
 
nigelmercier said:
That is not what the OP asked for.

Testing the capacity of batteries requires a very expensive bit of kit, nobody is suggesting that these devices can do the same job. They are useful for putting the battery under a fairly heavy and calibrated load, and testing the voltage. As such, they can detect a battery that is end of life, especially if compared with another.
Click to expand...
I am not sure that is entirely true. Its certainly true that the drop testers don't tell you whether deep discharge batteries have any capacity for domestic use on a boat.

However you can test the capacity of batteries with a known load (say a couple of car headlamp bulbs) and a multimeter and a little patience. (I assume that you have a battery charger to charge the things up with to start with.)

Charge the battery fully, place the load across them and monitor the voltage vs time. You can directly measure the capacity of the battery at the discharge rate you have applied. Not expensive - just a little effort and some cheap components.
 
nigelmercier said:
In your example, I would have allowed 24H after charging,
Click to expand...

Actually I did subsequently give it a boost charge and a couple of days float charge for curiosity, its capacity was still negligible but it would give a good high rate for a few seconds which is all a starter needs if everything else is favourable.

When I was in the battery industry we tried a number of devices for quick indication of the capacity of standby batteries and decided nothing gave a reliable indication other than a discharge test at realistic rate.

Other methods (voltage, s.g. etc) can give a good idea of the state of charge of a battery you know to be healthy but they don't tell you if the battery is healthy or not!
 
Last year I suspected that my caravan battery was duff as it wouldn't power the lights, pump etc for long before the charge indicator changed from green to amber. I had it tested at a garage with a load tester and it passed as ok. However, It still didn't operate properly so I replaced it. With a new battery the systems worked for the length of time you would expect. My conclusion is that these testers will tell you if your starter battery is ok but won't say anything useful about a leisure one. So plotting voltage against a known discharge in amps seems to be the only true test which, as someone has already said, can be done with a multimeter but takes time.
 
john_morris_uk said:
However you can test the capacity of batteries with a known load (say a couple of car headlamp bulbs) and a multimeter and a little patience...
Click to expand...

A few years ago I had a problem with a UPS unit that was brand new, but would only power my PC for about 20 seconds. I rigged up a test for the SLA battery much as you suggest, but the results were impossible to compare with the manufacturer's data. Then I had the idea of using a number of bulbs, connecting them in turn to keep the current reasonably constant. Eventually I was able to prove that the battery had about 50% of the stated capacity, and I got a refund. I needed two multi-meters, half a dozen bulbs, and two days. I did wonder if making an automated system with a microcontroller would be worthwhile; the idea is still on the back-burner, although I have obtained a current sensor chip.

Is this something that other readers would be interested in?
 
I have a friend in the sailing club who used to work for Lucas and has a battery tester which can be set for starter or leisure types, dialling in the CCA, Ah rating and type to tailor the test and results. It correctly showed which battery had lost capacity and was dragging the other one down. I guess this is quite a pricey bit of kit, but for a one-off it's probably best to find someone who has one and get them to do the testing - or spend two days with voltmeter and bulbs...

Rob.
 
cpedw said:
I made something loosely answering that description a while back. http://www.picaxeforum.co.uk/showthread.php?9547-Boat-project-4-Battery-load-tester The results were never very convincing when checking 12V, 100Ah flooded lead-acid batteries. It may give you some ideas (or steer you away from bad ideas?).
Click to expand...

I'd like to see the files, but I would need to register.

I was thinking of a PIC, one analogue input monitoring voltage, another monitoring current using an ACS712, four (perhaps five) digital outputs switching 10W, 20W, 40W, 80W loads.
 
If you PM your email I'll send you the pdf.
I used a Picaxe with Amploc Hall-effect current meter. The load was a 40W halogen bulb. Alternative loads could be plugged in if I had the bulbs. I measured the time from 12.6V to 12.2V while integrating the current. Based on 12.8V to 11.8V full to empty, the battery capacity was 100/40 times measured consumption. Crude I know but it was interesting to build.
 
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