Solved My charger said that the battery is 75% charged while it's connected to the van.

[joshhemming]

My van's battery is only a year old. I forgot and left the lights on overnight so the battery didn't have enough juice to start the van yesterday. A digital voltmeter showed only 3.5 volts. Instead of jump starting it, I hooked a Schumacher SC-1200A charger to it and charged it in-vehicle (with battery cables still connected) overnight. This morning the charger's digital display showed only a 75% charge and the green CHARGED/MAINTAINING light was not on yet. But the engine started fine. I drove it for about 8 miles, making a total of 3 stops. Each time it restarted fine.

Does charging a battery while it's still hooked up to the engine prevent it from charging to 100%? Or is my problem more likely a bad cell?

 

[shucker1]

I would give it a few more cycles to try and recover before I would say it's bad.

Best thing is to charge it and then let it sit for a day without charging so you get a more accurate result.

 

[BrooklynBay]

Did you check the voltage of the charging system with the engine running? The reading on the charger might be off since it's connected to the van. There's a constant current draw from the computer, and the radio memory circuits. Check the voltage with the engine on then take another reading with the engine off a few hours later.

 

[joshhemming]

I didn't do any additional checks because after driving it a couple more times over the past several days the battery is fine. The alternator has built its charge back up and is holding it.

I think the 75% reading that morning was due to it just needing more time to charge, since it was really drained.

 

[shucker1]

Glad it worked out.

Remember an alternator is not designed to recharge a completely dead battery.

It's best to put a good charge on it overnight, let it cool for several hours and then test.

 

[BrooklynBay]

Thanks for the update. Your thread is now marked as solved.