Battery Status

[C00P]

Bought a second-hand van that has a Breakaway system for the electric brakes.
The rechargeable battery is a 7Ah Lead-acid (Gel).
Thought I'd do a load test on it to see what state it was in.
Charged it using a staged charger set for Lead Acid and Motorcycle size battery.
Then connected a tail light globe that drew 0.41 amps and a voltmeter.
The voltage fell below 12 after 2hrs 40 minutes, and hit 10.5 after 3 hours at which point I terminated the test, figuring the battery was essentially flat.
This struck me as a pretty poor performance. I would have expected at least 10 hours at that current (10 x 0.4 = 4Ah) before the voltage fell that low.
Can any experts out there confirm my suspicion that this battery is well past its use-by date?
Cheers

Coop

[bee utey]

Ah or Amp-hours for a lead acid battery are calculated at a current that discharges a battery in around 20 hours, so a 7Ah battery would have to discharge at 7/20th of an amp or 350mA to get an accurate Ah figure. It can drop to 4Ah if drawn down at 4A, due to losses in the battery as heat. In any case your test is near enough and shows the battery is on its last legs. For safety's sake I'd suggest a top brand replacement, Panasonic was always a good brand.

[C00P]

Thanks, that confirms my theory that it should have been able to sustain 400mA for a lot longer than it did. Thanks for the formula, will remember that when I test the main batteries in the van.
Cheers

Coop

[drivesafe]

Hi C00P and your battery is cactus and will not meet the requirements of the standards.

With a small load like what you used, as bee_utey posted, you it should have run for about 9 hours time before discharging down to 12.0v.

Furthermore, not only will the battery not meet the minimum requirements, but if you did a full breakaway test by pulling the breakaway pin, you would probably totally stuff that battery in a few minutes.

You will need a new one before you do any towing.

[C00P]

Thanks, Drivesafe. I'll certainly replace it before the van hits the road. I can't see the current unit providing enough power to keep four brake units activated!
Hopefully it will never be needed!!
Cheers

Coo