The Stovebolt Site Forums The Shop Area The Electrical Bay Backwords Battery - Reversed

I thought this 12v battery was AFU inside cause I would try to charge it and nothing would happen.

So I put a meter on it for a volt check and found out it was reading a - 12.5 volts.

Seems I remember if a battery was dead and u hooked up a charger in reverse it could be charged up in reverse.

How it got that way I don't know, I pulled it out of my trailer for the winter and it seemed to be dead.

Question is....can it be put back to normal ?

Dan

yes, battery polarity can be reversed, but you will not revive it - any battery dead enough to accept a reverse polarity is scrap, I'd suggest sending it off to the recycler, exploding batteries are no fun .... and if that battery was part of a battery bank in your trailer, check the others

Bill

i also found that out with a CB radio i was testing out for the south bend run. ooops my bad. that pile over the bank is starting to get big

Uhhh are you sure the meter leads were correct on battery? If it is dead it should not be reading 12.5. Maybe 7 10 or ??

If you are going on just the fact it wont charge - MAYBE it is already charged.

The first thing I would do is check with a hydrometer. Then I think I would put a light on it and see if it hase enough to lite the lite.

Now then if you have reversed cell(s) no you cannot reverse a reverse cell to make it a foward (???) cell. If a reversed cell it is scrap.

The other common cause of "dead" battery is sulfation - especially so when they sit for a year or so
OR if the charging voltage is not high enough to fully recharge them. This can be salvaged but you will need to charge at a high voltage ie 15 or so for long time.

Dan Bentler

Ya the test leads were on correct, not totally believing the digital I got out my old trusty Simpson 260 analog and it said the same thing. Hard to believe it was backwards !

In the beginning I assumed it was dead cause it wouldn't take a charge and it was when I hooked up a newer type charger with fancy lights and the light lit up saying Check.

Check, check what? I don't have the manual for the charger cause I got it at an auction.
Check, okay I'll check it with a meter, and thats when the reversed polarity showed up.

I spose I could just re-mark the polarity on the top of the battery and live with it till it dies, ya think ?

Dan

Yes, a battery will charge backwards, but it can be revived.
Attach a load such as a headlight sealed beam, and run it down until the light will not burn at all. Polarity on the bulb doesn't matter, it's just a load device to drain the charge. Once the light goes out, connect a charger with the proper polarity observed, and charge the battery at a 5-10 amp rate for several hours. Check the specific gravity every hour or so until there is no difference in the reading for 2 or 3 consecutive checks. At that point, the battery has accepted all the charge it can take. Any further charging just boils water away. Full-charge specific gravity on an automotive battery is somewhere in the 1.265 to 1.300 range, depending on the original strength of the acid and how much loss of plate material off the grids has happened. Some of the capacity of the battery will be lost due to the reversed charge, but I doubt that it will be totally junk unless it was in very bad shape to begin with.
Jerry

Jerry are you calling the light bulb "drawdown" a reverse charge?

I was taught this is discharge. In the test you described this is normal battery operation and should do as described.

Reverse charging a battery in my mind is hooking it backwards basically charging with current in the same direction as that when battery is discharging. I would think this would destroy not only the battery but also most common off shelf chargers.

Most common cause of cell reversal is discharging battery until lowest cell hits 1.51 and continuing the discharge.
The lowest cell can reverse and will show reverse polarity compared to other cells. This is not recoverable.

Dan Bentler

I have recovered several incorrectly charged (reverse-polarized) batteries by completely discharging them, and recharging slowly with the charger connected with the proper polarity, so don't make the blanket statement that it's impossible. That situation usually happens when the battery has been totally discharged by leaving headlights on all day, and some dummy connects a charger incorrectly when attempting to recharge it. If the battery is still in the car, it becomes very obvious that things aren't right because the alternator rectifier diodes burn out. If the battery is totally dead, and is removed from the vehicle for charging, it's possible to charge it with the poles reversed. The lifespan of the battery is shortened, but I haven't noticed any serious compromise of cranking amps, etc. once it is fully discharged and recharged with the right polarity. The process is similar to the procedure for breaking down a badly sulfated battery, where it is repeatedly discharged and re-charged, causing the crystalline lead sulfate to re-dissolve.

Anytime an automotive cranking battery is discharged below 75% of its full-charge capacity, it will have trouble recovering a complete charge. That is the main difference between cranking batteries and deep-cycle batteries intended for forklifts, power wheelchairs, trolling motors, etc. Those batteries can be discharged to 25% of their total capacity and recharged without damage, but they cannot provide the heavy surge of current necessary to run a starter motor. Cranking batteries are designed to provide a short surge of heavy current, and undergo a fairly quick recharge to full capacity. Deep-cycle batteries discharge more slowly, and require a relatively long, slow-rate recharge.
Jerry

Well I do not pretend to know a lot about fixing screwed up batteries.

I suppose I can thank the people who trained me as a submarine electrician. I seem to have had few problems except normal depletion ie end of life and a screwdriver thru battery.

Dan

My first full time job 48 years ago was in a battery factory. We built about 1,500 to 2,000 automotive and heavy truck batteries a day. (that was a fairly small factory!)

The real education came while maintaining a small fleet of over-the-road trucks with four heavy-duty 6-volt batteries in each truck in a series-parallel arrangement. We kept a trickle charger bank going continuously and swapped out batteries four at a time when charging system problems would dead-line a truck for some reason, then recharge and test the take-out batteries and re-use the serviceable ones. The less road repair costs we had, the more profitable the truck line would be. Some emergency road service guys are real ripoff artists!
Jerry

Well thanks, Jerry, I had a feeling you'd come up with an answer for my problem.
The battery is Deep Cycle which came out of my flat bed trailer.

I'll drain it down and charge it back up, correct polarity and see what happens.

I just got one of those new type chargers ( Battery Tender )
It only has lights to tell me whats going on but according to the instructions it charges a battery at a bulk charge rate till it gets up to 80%, then it flips into a top off mode for the remaining 20%, When full charge is reached it flips into float mode which maintains the battery at full charge if left on the battery.

I'm thinking this charger is better cause I put it on a battery which I had charged with my old taper off type charger.
When I hooked it up it started at the bulk rate for a short time and then flipped into the top off mode.
It took about 12 hours at that rate for it to reach full capacity and flip to float mode.

I'm thinking it is a better charger cause I had thought the battery was fully charged, but after hooking up the new charger it told me....no ain't full yet, and finished the charge.

The biggest reason I bought the new type chargers was for the float or maint. mode so I could leave them hooked up up and not have to run around making sure all of my batteries are charged while they sit idle in the winter.

Dan

Is that the same charger that reversed the polarity in the first place? I think I'd be a little reluctant to try it again, unless the mistake was caused by connecting the charge leads wrong and the battery was so low the internal polarity protection didn't kick in. I'm firmly convinced the only effective way to check the state of charge of a battery is with a hydrometer, assuming you can get the cell covers off. All the voltage-monitoring electronic voodoo in the world is no ssubstitute for measuring the specific gravity of the acid.
Jerry

Gueezz Jerry, now u want me to go out and buy a hydro , whats a hydrometer ?
No, the charger, if it was me that got the polarity reversed, would have been my old taper off Schmacker charger.

I was kidding about the hydrometer, but I haven't used one of those since the 70's, back when batteries came dry and we had to pour in the acid and charge them up. We'd check the gravity to see if they were up to full, Hmmm, back in the 60's....Crap, I'm getting old !!

I'm guessing maybe it was me that got the bat reversed. The bat got real low and the compartment it's in only gives a side view of the bat with only enough clearance on top to get your hand in there. It was wired up with black leads for both terminals.

That's the story, thanks for the help, I appreciate it. I'll let u know how it turns out.

Dan

Things are back to normal, meaning the battery now has the correct polarity.
Thanks Jerry, I did like you said and ran it down with a sealbeam and then hooked up a charger.
Now here's where a little problem came up.....the battery would accept so much juice the leads from that charger got HOT.
I got another charger that has a kick out protection and hooked it up. I started with a 2amp rate and it would peg the needle on the charger for awhile and then kick out.
After about 6 hrs in that state it got to where it would accept a charge at a steady rate without tripping the overload cut-out.

I turned it up to a 6 amp rate and let it charge over night and came back to the shop the next day and the charge needle had dropped to low, meaning the battery was or could be fully charged.

Then with my newly purchased Battery Tender charger I hooked it up and finished the charge to 100%
Keep in mind....this is what's supposed to be happening, which is indicated by the grn, light flashing.
After some hrs. in this state the grn light stayed on, indicating full charge and the charger is now in the maintenance mode.
Jerry, I know if ur reading this, ur probably saying check the gravity in the thing, which I would love to do cause I'm curious also.......but the top on this battery is hard to remove, plus I don't have a hydrometer.
So, I guess I'll just put this battery back in service and see what happens.

Dan

It sounds like you're in pretty good shape, as long as there hasn't been enough cell plate damage to seriously compromise the current capacity of the battery. If the cell covers don't open up easily, it's possible there's some type of oddball electrolyte mix that can't be checked with a hydrometer anyway, so just give it a 15-second cranking check with the ignition disabled, and see if the terminal voltage stays up pretty well. I've used starters as high-load battery testers for some time when I don't have a carbon-pile load tester handy.

With a voltmeter attached to the battery posts, disable the ignition system, crank the engine for 15 seconds and watch the voltage. With the starter still running after 15 seconds, a 12 volt battery should stay above about 9.5 volts, or a 6-volt should maintain about 4.5 volts under the same test. There needs to be enough terminal voltage available to power the ignition even after an extended cranking period.
Jerry