Battery checks [flat battery]

[dave friday]

Hi all,so what checks are needed?
My dodgy battery, hydrometer cell readings are all near the top of the scale.
But the battery will only manage two starts before showing of a flat battery[wont manage the third start].
When I then put it on charge I get a reading of 7amps..after 12 hours it reads 1 amp.
I presume the plates are all gunged up?
Anyway,what gives?
Ta.

[123-jn]

You need to do a load test on it after charging it. Places like Halfords and Auto parts shops will do this for you if you haven't got a load tester. IT puts a massive resistance wire across the battery and reads the batteries reaction to being asked for all that power. If it can hold a decent voltage without dropping for 10 seconds it passes. Yours will probably gradually drop while the load is applied. New Battery required. I have an Exide 100 battery from Ebay in mine.
http://www.ebay.co.uk/itm/Exide-100-EB7 ... 2a4d70bba1" onclick="window.open(this.href);return false;

[dave friday]

Thanks 123-jn,good advice..i bought an Exide 80ah,it was a bit of a squeeze getting it in [107euro!]
Van goes brum straight away now!!

[VWMAK]

Was parked up in a field site at the weekend with a few other campers (friends), in the morning moved my car about 20m, started fine no issue.

Went to start it 10 minutes later flat battery, completely flat. Jump started it and it took a decent amount of time to come back to life. Then worked fine.

Very strange, how could the battery go flat in 10 mins? Nothing on. No switches flicked from the night before.

[Fudgy666]

When I then put it on charge I get a reading of 7amps..after 12 hours it reads 1 amp.

This is to be expected when charging any battery and is normal. As the voltage of the battery rises due to charging, the amount of current drawn will decrease.

The more discharged the battery is, the higher the initial current draw will be when it is put on charge.

V(voltage) = I(current) x R(resistance)

The (R)resistance of the battery is fixed, so as the (V)Voltage Difference between the battery and the charger decreases (Due to charging), the (I)current must also decrease.*
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.
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I think



*Dislaimer: It's been a few years since I sat my physics GCSE.

[kevtherev]

Was parked up in a field site at the weekend with a few other campers (friends), in the morning moved my car about 20m, started fine no issue.

Went to start it 10 minutes later flat battery, completely flat. Jump started it and it took a decent amount of time to come back to life. Then worked fine.

Very strange, how could the battery go flat in 10 mins? Nothing on. No switches flicked from the night before.

In 10 mins of running a weak battery will not absorb enough charge to do it again.
Or the ignition was left on.