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[ajg141]

I've been contacted by a friend who is having a strange problem with the batteries in his sub. I quote:

"I've been having drama's with my batteries lately.
 
As you are possibly aware I run two Sealed Lead Acid batteries both 6V 1.3 Ah. One runs the RC and they both are connected in series to provide 12v to the pump.
 
I bought a new battery just a week or two ago and charged it up. I then hooked it up the the boat and the motor just started running in reverse. I then switched polarity and the RC came to life.  For some reason the battery switched polarity. Since then another battery has done the same. I have no idea why. I thought It could have been the charger because of the second battery also reversing but I'm not sure now. Do you have any suggestions? Do you know how to switch it's polarity back. No one here seems to be giving me much help. Does anybody in your club know?"

As requested in the message I have asked around our Club - but with no real answers.

Could anyone shed any light on this for me please - any help would be gratefully appreciated.

Andrew

[malcolmfrary]

When a lead acid battery is made, the plates are both plain lead, and only get their coat of whatever it becomes (it WAS a LONG TIME AGO when I learnt the chemistry, and that learning has since fell out of the other ear) during the initial charging by the manufacturer, either within the battery or before.  It is in theory possible for a battery to be connected wrong way, completely discharge, form and re-charge to the opposite polarity, but very unlikely in practice.  I SUPPOSE it is possible for the manufacturer to put the wrong blobs of paint by the terminals, or even to use a different case top moulding intended for a different battery.
Odd one.  Anybody else got any good theories?

[Colin Bishop]

Found this on the Web relating to car batteries:

If a battery is fully discharged and continues to have a load, for example, leaving the headlights on, it is possible for one or more cells to reverse polarity. This is referred to as "cell reversal". To change reversed polarity, fully discharge the battery and recharge it with the correct polarity.

[ajg141]

Thanks for the suggestions to date. It has been suggested that if only one of the 2 'in series' batteries has run flat then the other (if still holding an adequate charge) could possibly reverse charge the discharged one. Anybody got any thoughts?

[Colin Bishop]

I have heard something to that effect as well. Possibly one battery suffered a cell breakdown which reduced its voltage but I'm only guessing.

[malcolmfrary]

If a battery has been reverse charged, I would have trouble trusting it again, especially if it was the main power source of a model worth many times the cost of a new battery.

[ajg141]

I certainly agree that the cost of a battery is of little importance when compared with the value of the sub and I too would be inclined to ditch both and start over again. Despite many a long trawl of the internet and lots of questions being asked of many learned people no real reason for this problem has been identified. However one interesting website has been found that gives a lot of battery info:  http://www.batteryuniversity.com/
It is possible to e-mail this site with a query - and this may well have to be done

[wingertaz]

I came across this situation about 6 months ago when a customer who had purchased a sealed lead acid battery on the net brought it into us to be tested. The battery had indeed been marked positive and negative incorrectly.

Gary

[Circlip]

       Bringing this one up again because my neighbors' 24V system (2X12V in series) has just proven to be a problem.
        He left waggon parked up for 2 months and over last couple of days has been trying to start it. He's checked
        the Batteries by 'Sparking' them and ok big blue flashes. Solved the problem an hour ago, yes you've guessed
        it, One of them HAS reversed POLARITY, these are not new and in the past were ok.