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magnoliafan89

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Have a car battery and wantedto know if it was any good. Got my fluke tester and set it to volts and put it across positive and negative...first battery had 0 volts and the second battery had 6 volts. Did i test these properly?
 

Pete999

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Have a car battery and wantedto know if it was any good. Got my fluke tester and set it to volts and put it across positive and negative...first battery had 0 volts and the second battery had 6 volts. Did i test these properly?
Got an ACT Battery tester for sale if you're interested
 

James

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Have a car battery and wantedto know if it was any good. Got my fluke tester and set it to volts and put it across positive and negative...first battery had 0 volts and the second battery had 6 volts. Did i test these properly?
They could both do with being charged before testing.
 

Charlie_

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Arms
Would have expected you to get 12 volts?
What condition are they in, dried up?
Best to just drive to a halfords or anywhere that offers free battery tests.
 
If they are 12V lead acid batteries and reading 0V and 6V, it's likely they are in a very sorry state and could be beyond redemption. Lead acid batteries tend not to like being discharged too far for too long and for a 12V battery, discharging to anything below around 10V can cause damage.

As above, a trip to Halfords or somewhere similar to get them tested and checked over might be the best bet.

Take care if attempting to charge them!
 
Be aware that a "proper" battery tester is needed to do a proper load test on it. A naff battery, once charged, can still show 12-14v but will drain very fast. Sounds like your batteries are flat - but even charged the condition would be unknown.
 
For years I have charged batteries for a day, and then tested, a load is required, and there are two methods, one looks at voltage decay the other at voltage recovery, in the main latter is better but needs a special meter to interpret the results.

However I have a energy monitor which logs what has happened, and I connected a smart charger to this, OK measuring input not output, but they are clearly related. I had a number of valve regulated lead acid batteries out of a chair lift, which had been discharged and left, clearly sulphated, and normally I would have said US. I had to put in parallel with a good battery to get charger to work.

So they sat there for a week doing nothing, at around day 10 they started to charge, saw the graph over around an hour go from zero to max charge rate sit there for 10 hours then drop again to zero. On testing the battery is was nearly in A1 condition, the same happened with the second battery of the pair.

This was not what I expected, I expected to see a gradual recovery, not act as if some one had flicked a switch after 10 days. Before the days of the smart charger I would not have dared leave a battery on charge for so long. After this I had a caravan 75 Ah battery which had been left flat, and again same result, it sat there for a few days it seemed doing nothing, then as if flicking a switch took a charge.

I also had a 20 Ah wheel chair battery, this seemed to do the same then completely failed, however it had been left discharged for two years.

The main problem is smart chargers will auto switch off with a sulphated battery, it sees them as open circuit, I was using a Lidi 3.8A charger, and it has 6 and 12 volt charging, it first checks there is a voltage, if there is no voltage it will not charge, if there is a voltage it tests how much, if under I think 7.8 volt it assumes it's a 6 volt battery, at 14.4 volt it assumes charged, and at 16 volt it assumes leads open circuit. I may have voltages slightly out but the point is they will not charge a completly discharged battery.

Putting a second good battery in parallel will kid it to maintain a voltage of 12.9 volt, as volts drop to 12.8 it will charge until 14.4 for maybe 1/2 a minute then off again, so 98% of time if you look it shows 12.9 volt. However if the battery on charge has a shorted cell, as the other cells recover it will discharge the donor battery, so the donor battery must not be too big, or the battery with shorted cell could explode. Same goes for charger, if too big and left unattended it could cause a battery with shorted cell to explode and until other cells have recovered there is not way of knowing if there is a shorted cell.

In other words there is some danger in what I did, I understand the dangers and using the PC to monitor although battery was in garage I could check state with phone, tablet or PC where ever I was, and remotely disconnect charger, and there was a limit of 7 Ah from donor battery.

But some 50 years as auto electrician I had never expected a battery would recover in that way, as said it was as if after 10 days some one flicked a switch. Without the energy monitor I would not have know this.
 

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