At 74 years old and farming, I've done a lot of wrenching on anything and everything. At some time or the other, I've run what I thought was every test possible on batteries. Recently, though, on another site, a person mentioned testing for voltage from the battery positive post to the top of the battery case. He did not state the purpose of the test or what it showed. I've never heard of such and can't find a mention of it in any manuals.

On the six larger batteries that I have working right now, three are nearly new and three are old. When I check voltage between battery positive and the case top at various places, the three newer show 0 volts. All three of the older ones show voltage ranging from 5 volts on one battery to 9 volts on another. All six batteries, though, are working reliably.

Can someone explain to me if this measuring of voltage from battery positive to case is a reliable test for anything and if so, what? Thank you.

 

Hmm?..That's interesting..Done lots of direct current/wiring/car stuff..so I'm curious ..hope someone can answer your question.

OH..i forgot to mention..74 uh?..me too....most everything is working good, but not my memory!! Hope I remember to check back
on the subject...!

 

I am not sure, but I vaugely remember that the OLD 6v batteries had a spot on each cell and that is what he may have been referring to. I think it was supposed to be a way to check each set of plates looking for a dead cell. Wont work on modern cases as they are all plastic of some sort and remember not storing batteries on ground because they will drain? Not an issue with the new batteries (I still put wood under them though).

Like I said I am not sure but I think that is what they were referring to??

 

One reason a battery will tend to lose voltage (slowly, though still significant over time) is due to dirt, grease, and moisture on the case itself. This sets up a conductive path between the terminals. That might be what that is referring to.

Windex (with ammonia) is pretty good stuff for keeping the crud off the battery case and neutralizing the battery box or tray from acid fumes. Batteries outgas in use and during charging.

 

I have a guy at work that says that you CANNOT store batteries on the ground. Because it makes them discharge. You have to put them on wood or rubber to "insulate" them from the ground and keep them from being.....grounded?

my point is, people come up with some pretty strange beliefs. Unless they are backed by something, just ignore it.

Remember, there are people in this world that drink their own pee because in their mind its "good for you"

 

Thank you all for your replies. I guess the question that is bothering me most is why I'm getting voltage readings between the positive post and the plastic case. I had always assumed the case wouldn't conduct voltage. Tedster9 mentioned dirt on the case, so I cleaned two of the batteries on which I'm getting readings. I used ammonia on the first cleaning and got the same voltage readings as before the cleaning. I then used a baking soda mix. Got the same readings. The readings are on the three older batteries. The newer ones are showing no voltage measuring from the positive post to the battery case.. They are all 12 volt batteries. If anyone ever has another idea of how this voltage is being measured through the battery case, please let me know.

 

It's cold in the garage right now, so I'm not gonna go check (Mañana) but you piqued my interest. Will report back.

One thing to keep in mind about voltage, it may be a very very low current, and while it would be best to see Zero volts, if it doesn't impact the battery or cause it to run down in 4 and half months, it won't matter. It could very well be the case you need to find something to actually worry about. These days, that shouldn't take very long at all.

What does the voltage read between the pos + terminal and the neg - terminal? Ten bucks says a good overnight charge wouldn't hurt anything. Winter's a comin', if it ain't already here.

 

Dirt & vapor deposits from a battery venting from flooded battery cell caps (or vent if doesn't have removable caps) as its recharged, form a conductive path across the top of the battery. This discharge path is what we're measuring & can be thought of as "parasitic" drain, SO, its a good idea for us to get & keep the case of our batteries squeaky clean. To keep it clean, If need be, I wipe mine down with the clean area of the towel I use when I check the engine oil.

To get it clean I use a base mix of water & baking soda to neutralize any acid. If dirt or oil, or grease is caked on, use a good quality plastic safe / no solvents cleaner, like Windex, or dish detergent, or the like, that'll get after any grease, oil or other under hood grime, thats friendly with the battery case material. Then once squeaky clean & dry, (no volt reading) when the DVM B- lead is passed in contact with & over the top of the battery case. We're more likely to get a reading closer to the cell vents & between the cells & where the top is dirty.
Once clean I'll spray a film of CRC Heavy Duty Silicone spray over the top of the battery case, to help keep it clean & put a dirt repelling high resistance insulator film on the case surface, that'll self heal if messed with, or when we choose to wipe the battery top down again. Once a year gets it done in my area.
Not very dirty where I live & I'd always kept my battery top clean, but was surprised the First time I did the measurement & got readings all over the top of my Ranger's battery case. The silicone spray does a good job of keeping it clean & the leakage lower & for longer.

Low maintenance, AGM or Gel cell batteries aren't as likely to have the problem, as there isn't as much venting of vapors like the old flooded cell battery with removable cell caps pumps out as its recharged, Anyway, its good practice & a good idea for us to keep the battery case as clean as possible, especially if we live close to or operate around salt water, or say a mine where its really dusty, or drive on unpaved roads, or well you get the idea, get & keep the battery case as clean as your of a mind to. I typically get between 9 - 11 years from my vehicle Motorcraft batteries & between 15 - 18 years on my Marine trolling & cranking batteries. Yup I use a Smart charger to keep the vehicle & marine batteries Fully charged & inside & Clean when not in use for long times, like winter. More thoughts for consideration