Ok I had never heard of this little trick. I wanted to share. If everyone else already knows then I guess no one really cares.
1. Disconnect battey terminals
2. Pop the cell covers off. BE CAREFUL BATTEY ACID WILL BURN YOUR SKIN
3. Useing a voltmeter place the black lead on the negative terminal. Then stick the red lead on the plates one cell at a time.
4. Good cells read 12 volts, bad cells read low like 2-6 volts. But dead cells read zero.

I checked my old batterys after replaceing them yesterday. I have 1 dead cell in one and both of them have low cells like 4 volts. Cool trick I thought I would share.

 

Yes, but using hydrometer is far more fun, watching the float rise up.
Plus I don't have to disconnect the terminals.
However, thx for sharing.

 

I also don't like dipping my equipment, DVM probe, in acid. Lot better, cleaner and safer ways to do it.

 

I use the Hydrometer

But never Heard of this trick Jim thanks for sharing

 

Great way to ruin a good set of test leads, no thanks.

 

Digital load tester... never look back.

Josh

 

Great info, especially if your Hydrometer got busted or your away from home (a DVM is always in my tool box).
One could make an extension for the leads if worried about corrosion of originals.

 

Hydrometer under 10 bucks
Good leads 30 bucks or more. Harbor Freights don't count however they could be the sacrificial lamb.

 

Hasn't hurt my leads and they suck. But whatever I just never had luck with a hydrometer. The one I had said the dead cell was 50%. This seemed a easier way to test the cells. And a 100% way to test em.

 

Hey Im going to try it Jim Im not scared LOL

All you have to do is Rinse the Leads Off in Water when done I don't think that's a Big Deal at ALL Honestly

If a Hydrometer Don't get rinsed out it may cause it to read bad

I have ruined hydrometers like this when I forgot to rinse them out But they Last if acid is cleaned out with water

The Battery acid is Brutal if it sits awhile for sure

 

You can get a cheap DVOM at HF for about $4. They're not worth crap for testing alternator diodes or for AC current in an alternator but good for testing continuity and easy junk. I'm like you though, I wouldn't stick a set of Fluke leads in a battery.

 

theres 6 cells in a battery @ 2.2v each. 1 bad cell and your battery should read about 10.8v.
not to mention they always sound funny while cranking on a dead cell

 

My take on this is that it's a valid test. As a teen I sometimes hung around a wrecking yard and the old guy who owned the place always checked batteries like this. According to him, the point was many batteries are bad because a heavy handed mechanic (sic.) hammered on the terminal and broke the connection to the first plate inside the battery case. I thought I remembered putting one lead on a terminal and starting with the nearest cell you should get 2.sumthing volts (depending on state of charge) it might read negative volts depending on where you start and which leads you put where but it really doesn't matter. Moving to the next cell you should get 4.sumthing, next should be 6.sumthing and so-on. If all the numbers are low put it on a two amp charger overnight, let it rest a couple of hours and retest. If one cell is significantly lower than the rest (say .4 or more) it went in the scrap pile.

I should note I haven't done this in a few years. I think a load test is easier, more accurate, and there's a place just down the street that will do it for free.

Also, if I was suspicious of a battery and couldn't get to the parts store for some reason, I would use my MAC EM710 multimeter to record cranking voltage (not put the leads in the battery). If the battery was recently charged and dropped below 9.5v or so, it's getting replaced. (And I'll diagnose the bad starter with the new battery lol (just pointing out the possible flaw in this plan))

Yes, I sub idea'd a sub idea.