Testing a suspect leisure battery.

[Obanboy666]

I recently replaced my pair of leisure batteries after one or both died on me on a recent Scotland trip. First night away after both batteries were fully charged with a Ctek charger the voltage dropped to 10.5 volts within 1/2 hour of having the Truma heating on.
Both replaced and have had no problems wilding over the last month.
I have charged both suspect batteries and have a 12v 50 watt bulb that I can rig up and fit to the battery. The batteries are Yuasa 110 amps.
Being a complete numpty regarding electrics, approx how long should the bulb stay on before dimming due low voltage ? I have a multi meter and know how to check voltage, should I be checking the voltage say every hour ?
Any advise would be greatly appreciated. I suspect one of the batteries may be ok and once I know which it is I can use it in an emergency.

 

[harrow]

So you bulb takes roughly 4 amps, but it depends how much you want to discharge the battery your testing, because the bulb will still glow.

If you discharge the battery under test to 12 volts from fully charged and compare the time with each battery and see which one is better ?

 

[molly 2]

If you suspect your LB are shot ,you are probably right .

 

[Obanboy666]

Just checked first battery on test after 2 hours, voltage down to 8.5 so reckon that’s the duff one. Second hopefully ‘good’ battery now on test, will check voltage every hour.

 

[wildebus]

I recently replaced my pair of leisure batteries after one or both died on me on a recent Scotland trip. First night away after both batteries were fully charged with a Ctek charger the voltage dropped to 10.5 volts within 1/2 hour of having the Truma heating on.
Both replaced and have had no problems wilding over the last month.
I have charged both suspect batteries and have a 12v 50 watt bulb that I can rig up and fit to the battery. The batteries are Yuasa 110 amps.
Being a complete numpty regarding electrics, approx how long should the bulb stay on before dimming due low voltage ? I have a multi meter and know how to check voltage, should I be checking the voltage say every hour ?
Any advise would be greatly appreciated. I suspect one of the batteries may be ok and once I know which it is I can use it in an emergency.

Bit of quick maths …
Yuasa will usually quote their capacity at the C20 rating - i.e. enough current to fully discharge the battery in 20 Hours. so for a 110Ah Battery, that would be a constant 5.5 Amps/Per hour - or around 66W - so about 15% more than your 50W Light Bulb.
Typical Recommended Discharge is just to 50% of Total Capacity of course, so if you leave the light on for around 11.5 Hours you should ideally be at 50% charge.

Using those Voltage tables you can find on the internet, a typical Lead Acid Battery at 50% charge will read around 12.05V.

So you could do the following with your meter and test bulb:

1. Apply a full charge on the battery
2. Leave for a a few hours (or maybe overnight) and check the voltage - expect at least 12.7V
3. Add the 50W load and leave on for 11.5 Hours
4. Remove the load and then let the battery settle for around 1-2 hours and check the voltage - if over 12.05V, it would seem to be fine; if under 12V, it is suffering a bit; If a lot under 12V, probably shot.