The only way a battery could be reverse charged is if it was dead when it was attached to the charger (or brand new and never charged). Sounds like that happened here. I wouldn't trust that battery after that sort ordeal. It would have to cause chemical changes to the plates that are unlikely to reverse completely. In a normal battery, positive plates are made of lead dioxide, negative of pure lead. reverse charging would cause oxygen to migrate to negative plate. Then recharging would push it back. That's in addition to the battery having excess sulfation due to being fully discharged, not to mention heat damage from the recharging process. What you end up with is a questionable mess.

As for damage to the car, if there's a master fuse or fusible link, that would protect everything. That isn't the case with older Benz cars. The alternator is connected at all times, so that's where I would expect first damage. When the connection is "normal", the alternator diodes block current flowing back from the battery. Reversed, and the battery would essentially discharge through the alternator stator and diodes. If that goes on long enough, the alternator would cook off. If you turned the key, then the possibilities are endless.

The more I think about it the more I question the original post. I am not sure you can connect a battery to the opposite poles on a car.

Have you ever used jumper cables and mistakenly touched it to the wrong pole? The spark will make you drop your teeth.

If this were connected to the wrong post, why not the huge spark????

As MxFrank said above, a reverse connection results in a flash due to the dead-shorting through the alternator diodes. At a very minimum, the OVP relay should have popped. There are a few posts on this forum (including one relatively recent) that had that happen.

I also question how the battery could be charged backwards. Someone would have to be seriously dumb to connect it backwards, everything is color coded and marked with + and - signs. On top of that, the battery would have had to been completely flat....as in 0V to even take a charge in reverse, most "dead" batteries still have at least a couple volts present. Any charge at all would have dead shorted through the diodes in the charger and possibly damaged it or the battery. Most modern chargers have some sort of sensing circuit to prevent charging in reverse.

Lastly, if the battery really were that dead and self-discharged to that point on its own to get there, it's toast. The plates will be heavily sulfated and likely has a nice layer of crap in the bottom to keep discharging it. A battery that's just sitting will self-discharge, but shouldn't go completely flat unless it's already in poor condition internally. Good practice says that a battery that's going to sit long-term should be connected to a trickle charger/maintainer anyway. A cheapie from Wal-Mart is about 1/8 the cost of a new battery. Money well spent.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Any comments always much appreciated! post #1


Some times this forum really makes me smile.

__________________
Paul

I must self report to the mods that I'm harassing the poster and demand that my account be locked and deleted.

"Puzzler" is an appropriate moniker. I read his initial post three times and still didn't understand it. Ah well, it takes all sorts.

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown