Battery alternator question

[stinkbelly]

My sister in law has a lexus with a 6 month old battery. It has been sitting unused for about 2 months and it looks like the lights were on. The battery is dead. I jump started it and drove it around for about 30-40 minutes. I turned it off and then tried to turn it back on and it was dead.

So how long will it take for an alternator to charge a totally dead car battery (with all electronics in the car off)?

Will a dead battery that is sitting for a couple of months ever be good again?

[denimdeerslayer]

It would be better to slow charge it for a while and then see if it will hold a charge.

[randal]

I would think if it's the first time the battery has ever been completely drained it would be ok.. take it to the auto store drop it off and let them load test it..

[blntrey3]

Trickle Charge is all I can think to help

[wal1809]

To be sure that she doesn't get stuck out I would take it and have it charged and load tested.

See you a few weeks.

[fishingsetx]

Quickest way to kill a battery (other than physical damage) is to let it sit for a while fully discharged. Trying to charge a dead battery with the alternator is a good way to fry that too (although we have all done it). Id bet the battery is toast. Fully discharging it is bad for it, leaving it that way will kill it quick. If you could drive it, the alternator is probably still good. Every time ive done it, it only took 10-15 mins driving to have enough charge to restart the car.

Do you have a multimeter?

Patriotism is supporting your country all the time, and your government when it deserves it. - Mark Twain

[stinkbelly]

I do have a multimeter and a battery charger. The car is at my house. I wish I would have hooked up the charger last night.

[ladrones]

Is it a AGM battery?

[stinkbelly]

I am not sure if it is a gel or AGM battery or not. How do you tell? It is an interstate and the car has plastic coverings over everything. All I can see is the top without removing all the coverings.

[fishingsetx]

I do have a multimeter and a battery charger. The car is at my house. I wish I would have hooked up the charger last night.

Check the voltage on the battery, then start the car and check it again. The alternator should be putting out 14v or so. If you drove the car for that long and the alternator is putting out 14v, it should be ok. If it is less than 14v, you can unhook the battery and check it again. you can try charging the battery, but id just replace it if it was me. Being that it was that discharged, I wouldnt trust it.

Everything you describe points to a bad battery, but there is a VERY small chance the alternator is failing. Check the voltages and post them up

Patriotism is supporting your country all the time, and your government when it deserves it. - Mark Twain

[stinkbelly]

I will do that tonight.

Thanks

[stinkbelly]

I am getting 13 v for the battery and 13.5 v running with my little meter. I took it to O'Reilly and he said the battery is good and the alternator is putting out 13.2 volts. He also said the alternator failed one of the checks but I forget which one.

[fishingsetx]

You charge the battery? Earlier, you had said that the car wouldnt crank. 13V should be nore than enough. 13.5V sounds a little low for the alternator output.

Patriotism is supporting your country all the time, and your government when it deserves it. - Mark Twain

[AJMag]

Alt is fine. Should be 13 to 13.5. Pop the caps off and check the liquid level. If the battery is showing 13 and it still wont start, then it's lost the cranking amps, which should show on a battery test if they actually tested it all. I'd warranty out the battery regardless.

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[stinkbelly]

I got it to start and drove it around