Did I kill my battery?

Last sunday I went to start my truck & the battery was dead found that I had left the gps & xm charger plugged in. I put the battery charger on the battery at a 2 amp slow charge. I was in a hurry when I did it as it was cold in mid 20’s & wanted to get back inside where it was warm. 8 hour’s later I went back out to check thing’s & the battery was still dead I looked thing’s over & found out I had hooked the charger up backward’s positive on negi & neg on positive. I then swapped out the battery from my other truck & left the dead battery set for a day & put the charger on the right way & about 10 hour’s later it got up to 13.5 volt’s. My question is it safe to use this battery or would I need to put it in reversed because or the reverse charge the 1st time?

How long were the GPS and XM chargers running? A healthy battery could run them for days and still start the truck.

Get the battery load tested. Many auto parts chain stores will do this for free.

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The charger’s were running overnight I have left them on before & this is the 1st time the battery went dead not even enough charge to click the starter solenoid. Can it be load tested out of the truck?

Sure, bring it to your local mechanic and they will test it for you.

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When you hook a battery charger up backwards, instead of the charger putting energy back into the battery, the charger removes any energy that was in the battery.

So the battery is now completely dead, and needs to be replaced.


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would they be able to test for damage from reverse charging?

Thank you that is what I was afraid of.

Once a battery is fully discharged it will take a reversed polarity charge but it will never accumulate much amperage and it is very unlikely that the battery will ever take a full charge if discharged and then correctly recharged but what will it cost to try? Connect a headlight or some similar load to the battery and operate it until there is no measurable voltage remaining and then connect the charger and leave it for a day or so and hope for the best. I would place about as much faith in such a battery as I would a teenager bringing back all the change from a trip to the store.

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Thank you I will give that a try but will possibly end up getting a new battery as I don’t think I will trust the old one no matter how it turn’s out. That remark about the teenager sound’s like my ex wife & daughter.

I’d remove the battery and just charge it up with a battery charger at the 2 amp rate for 20 hours at least, then take the battery to a shop for a battery load test. If it tests ok, me, I’d have no troubles to use it again. Sometimes the manufacturer will accidentally charge up a battery backwards at the factory. A battery can indeed be charged backwards. So it’s always a good idea to check the battery polarity before installing a new battery, as you might be the unlucky one to purchase a reversed charged battery and when installed, in turn damage your car’s electrical system.

BTW, it’s possible you did some damage to the vehicle, when you hooked your battery charger backwards with the battery still connected. Don’t go on any long trips until you know the alternator keeps the battery charged.

No damage was done to the truck it’s a 1990 so very few electronic’s the alternator is putting out 14.5 volt’s every thing is working like it is supossed to.

That’s very good news. Hopefully you’ll even be able to return the battery to service.

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Like I said it is a1990 F150 & you know first hand how tough the older Ford’s are.

Yes, yes I do :slight_smile:

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If your 2 amp charger is fairly new, it maybe be a battery maintainer/charger. If so, it would not reverse charge a battery, it also will not charge a completely dead battery either. What ever you do, do not put the battery in reversed, you will damage the truck that way, even a 1990 Ford.

The fact that the battery went dead with such a small load on it tells me that your battery was on its way out anyway. It may hold a charge long enough to start your truck and take enough of a charge each time the truck is driven for the next start, but it won’t do that for long. I would not trust it if you rely on this truck for your livelihood.


When a battery is connected incorrectly there may be little or no damage if the key is not turned on. Even a 28 year old Ford could be $eriously damaged if the polarity is reversed and the key is turned on and starting is attempted. From my experience that situation results in the ECM and fuel pump relays failing and several fusible links burning out. If lucky the fusible links would pop before any wiring was toasted if not the ECM would likely be lost.

An early 90s Firebird was brought in years ago with the battery reversed and when I estimated $2,000+ for the visible damage and couldn’t guarantee that would be all that was needed the owner drug the car away. There was a great possibility that the instrument panel and the harness to it was damaged which would have pushed the price well above the cars value.

I doubt that any damage was done to the battery…no matter how long the charger was on it.

All chargers have it built in, that if a battery is connected with reverse polarity…the charger will trip off.


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Not all battery chargers have reverse polarity protection.


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I will be getting a new battery as I don’t know how old it is & also a brand I never heard of before ( econocraft ) it was in the truck when I got it.