I have been in some discussions recently and we talked about dead batteries. I had mentioned how to use a voltmeter to check for a dead cell. I’ve had a PM asking how to do this. So here goes.
I learned this when I worked for Sears’ Auto Center back in the late 70’s. This will not work on “sealed” or “maintenance free” batteries, only on batteries that have accessible cells. I’m using an old car battery hijacked from my neighbor
for illustration. The voltmeter in the pictures is from Wal-Mart - $10.00. That and a $2 test light will find most your electric trouble if you take your time and think it through.
Battery voltage is 12.22 – not the greatest – but not that bad. The lids are open so that I can access the cells. I use a nail with my leads so the acid doesn’t eat my leads and I need to get down pretty far (on a car battery) to touch the cells. You only have to touch the lead cells – don’t “stab” them.
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Keep the red lead towards the + post and the black lead towards the – post. Test from + post to first cell and the reading is about 2.03 volts. If you divide 12.22 (battery voltage) by 6 (# of cells) = ~ 2.04 volts per cell. An obviously low reading or a negative reading is indicative of a bad or a shorted cell and the battery needs replacing.
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Then test from cell 1 to cell 2; cell 2 to cell 3; cell 3 to cell 4; cell 4 to cell 5 and cell 5 to cell 6. They do not have to be exact – just reasonably close and it is common for some fluctuation in tenths of volts.
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When you test from cell 6 to the – post your reading should be “0” or something in the low tenths, even a negative in the low tenths will be OK. You can switch the leads around then (red on negative post and black in cell 6 and verify a negative reading). All this battery needs is a long slow charge.
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BTW, being an ultimate cheapskate, I have used this for years to find “~ good” batteries for my boat from stacks of batteries discarded behind parts houses…that would be parts stores for you Yankees! They would last a whole summer and sometimes a couple of years!
In case anyone is wondering how I got 3 hands; I was assisted by the lovely and gracious "Snickerdoo", world renown Chef of butterscotch pies.
I learned this when I worked for Sears’ Auto Center back in the late 70’s. This will not work on “sealed” or “maintenance free” batteries, only on batteries that have accessible cells. I’m using an old car battery hijacked from my neighbor
for illustration. The voltmeter in the pictures is from Wal-Mart - $10.00. That and a $2 test light will find most your electric trouble if you take your time and think it through.Battery voltage is 12.22 – not the greatest – but not that bad. The lids are open so that I can access the cells. I use a nail with my leads so the acid doesn’t eat my leads and I need to get down pretty far (on a car battery) to touch the cells. You only have to touch the lead cells – don’t “stab” them.
Keep the red lead towards the + post and the black lead towards the – post. Test from + post to first cell and the reading is about 2.03 volts. If you divide 12.22 (battery voltage) by 6 (# of cells) = ~ 2.04 volts per cell. An obviously low reading or a negative reading is indicative of a bad or a shorted cell and the battery needs replacing.
Then test from cell 1 to cell 2; cell 2 to cell 3; cell 3 to cell 4; cell 4 to cell 5 and cell 5 to cell 6. They do not have to be exact – just reasonably close and it is common for some fluctuation in tenths of volts.
When you test from cell 6 to the – post your reading should be “0” or something in the low tenths, even a negative in the low tenths will be OK. You can switch the leads around then (red on negative post and black in cell 6 and verify a negative reading). All this battery needs is a long slow charge.
BTW, being an ultimate cheapskate, I have used this for years to find “~ good” batteries for my boat from stacks of batteries discarded behind parts houses…that would be parts stores for you Yankees!
They would last a whole summer and sometimes a couple of years!In case anyone is wondering how I got 3 hands; I was assisted by the lovely and gracious "Snickerdoo", world renown Chef of butterscotch pies.
