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.
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.
Thanks Gumby! Great pics. Nice presentation. I've got a "T" cell that I'll try this on. Replaced it because it didn't want to hold a charge. Maybe I was wrong.
Thanks
Rocksolid
I swear maybe I'm the only (?) one out there who gets this BUT.... can have a conventional lead-acid battery with perfect cells, great Hydrometer (gravity) readings, voltage readings, and the ALL the planets and stars IN alignment, and STILL have it fail under load! Needless to say I've pretty much given up on all of these efforts these days. I just simply put the (car) battery on a ‘LOAD Tester’ - pass it stays, fail it goes. As far as motorcycles I now have ALL of em' with 'for real' SEALED gel and/or AGM batteries. I never EVER want another vented and removable cap regular ACID-filled battery within even a mile of another motorcycle, ever! The amount of money saved alone on ruined clothes and parts easily pays for em'! Add to that, "an ounce of prevention being worth a pound of cure": Now all my bikes are immediately put on a (not trickle but...) 'Float Charger' whenever they are not being used. I just can't believe how amazingly well these work!!! Battery Life is increased to years and years as opposed to a couple (if your lucky?) years. NOW if only I could get a decent for-real sealed batteries (not just a 'pretend' sealed batteries!) for our trucks and car?! Man, talk about livin' on easy street?! Nuff' said.
Footnote: Natch, for those living in a warmer climate or at least having (dream my dreams…) a for-REAL heated garage to work in, the above sure may not apply. But for the Mid-West ‘Artic Circle’ of the U.S. (South Dakota)?! You better believe it!
Tks Gumby for the info on testing a battery,I did the test and my battery was reading 13.2
1st-2.1
2nd-2.0
3rd-2.3
4th-2.3
5th-2.1
6th-0 so i guess my battery is allright there`s a few a little higher than 2.0
But i think that`s ok.Tks again,Jeff
Well, I'm not a battery expert, so here are a few things and questions:
1/ Wouldn't it show less than 12V if you have dead cell(s)? This leads to the next thing:
2/ What would you do when you find dead cells? I mean most of the batteries' top covers are sealed, so if you'd take it off to replace the cell and not careful resealing it it'd be bad just like LGR said.
3/ Then again, if you don't replace dead cells but instead throw the dead battery away, then (just like LGR said) why not just put it on a Load tester or simply just a charger (one would indicate if the battery's bad or not) and know if it's ... well, bad or not?
Like I said in my second paragraph, if you have a sealed battery you cannot perform this test. Unless you have someone to do the load testing for you (Autozone is 30 miles from me), or have your own load testing equipment then you're stuck doing voo-doo.
If you have a bad cell - you have to replace the battery. I've not heard of any method for "replacing a bad cell".
For Jeff's example I'm confident that he can give it a good trickle (slow) charge and it will be fine. This is only a definitive test that if the battery fails - replace it.
Gumby - I was talking about the top covers, not the caps, but since "replacing the bad cells" is not an option then that doesn't matter
My battery charger does show if the battery is bad or not, also I'm pretty sure even if it doesn't show (on weak batteries) after charging the voltage will be below 12V (it works on rechargeable AAs and the likes)
Tks Gumby for the info on testing a battery,I did the test and my battery was reading 13.2
1st-2.1
2nd-2.0
3rd-2.3
4th-2.3
5th-2.1
6th-0 so i guess my battery is allright there`s a few a little higher than 2.0
But i think that`s ok.Tks again,Jeff
You can hook your battery up to a vat40 tester and put a load on the battery, the cell that bubbles is the bad cell. I believe autozone uses those testers and most garages.
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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.
