Battery Pole Polarity Reversal

I left the switch on my M715 contact maint. truck, ran the bat. all the way down! I hooked one up to the charger no problem. I just hooked up the second on and the chrager is saying the polarity has switched, so I hooked it up in reverse pos to neg and neg to pos and it is charging fine? Anyone every experienced this before?!?!?!?!?!?!
James G.

PS: How do I reset the batteries in the truck, I don't want to burn anything up!

I'd say either the battery is bad or some thing is wrong with the charger. I would never hook it up that way. Always hook red clamp to pos and black clamp to negative as written on the case. Easiest way to hook them back up is take one battery and put it in truck and hook the pos cable to pos terminal. Then take the second battery and hook the neg cable to the neg post on that battery. Then take the crossover cable (the cable with 2 battery clamps on each end) and hook it up to the remaining 2 post.

I have checked the charger with a couple of other batteries I have and the charger is fine. But when I hook up the one battery from the truck the charger gives out a steady tone and tells me to reverse the cables for correct battery polarity. The polarity has has changed on the battery the pos post is now negative and the negative pole is now positive!
James G.

Did you remove the cross-over cable?

Lead acid batteries aren't too particular about polarity. If you can draw the reversed battery down to dead again and recharge it the correct way you might find that it'll come back but it needs to be absolutely dead flat before you start the charging process. Hook up that battery alone and turn the lights on; don't try a quick discharge like one of our mechanics did... with a crescent wrench across the terminals.

Its true this can and does happen, Ive done as above, drawn it down to dead and start over, its important to remember thata 1.5 amp is the ultimate charge rate, it takes time but it is the healthiest charge that will last the longest, Ive also just put it on and eventually it will push thru and start charging correctly, done both.if its a good bat it will be fine as long as U maintaine it, all bats drain 1/2 to 1 amp a month if not used ..to cold or hot is equally bad and will discharge faster, cement floors mean absolutly nothing , other that it may be colder and then of course it will discharge faster, Ive called all the bat manufacturers over the years and this has alwasys been the same from all the techs, and i have for 30 years had a dozen or so bats to maintain, keep em clean, and as Bjorn has said, the best way to charge multi bats is to do em individually, at a slow amp at a good temp, and a clean bat,do this twice a year to all bats, and keep em on a maintainer/charger when not used for more than 4 days, thats recomended. Randy

actually I mean its already drawn down,or it would not have reversed, just charge it, and it will more than likely take it eventually. randy

dang chargers are getting too smart.

Yeah, if there's even a hint of a charge left in the battery, the charger will sense it and give you the reversed polarity warning.

Can I just run the battery with the polarity reversed for the time being, just remembering to hook it up in reverse?
James G.

You probably burned the coil out on the M715 too by leaving it on all night. Just givin you a heads up incase it doesn't start after you figure out the battery problem.

I did the same thing to a M725. The batteries were low from sitting too long, put a 12v charger on 1 battery without unhooking the inter battery cable and came back and the other battery had a reverse charge. I just unhooked the inter battery cable and put the charger on the other battery. It drew a high charge current for a few min but then charged normally. Now that I think about it, I may have put some kind of load like a light across it to get it almost discharged. I was using an older battery charger.

I wouldn't use it reversed, you will probably ruin the battery and you might damage your alternator.