I have a 12volt battery for my car. I just bought a small charger. The battery appears to be dead. I set the charger to 2amps- approximately how long does it take to charge? is this better to set it to 2amps or should I go to 10? Thank you very much KOS
It takes a long time, and letting the battery discharge completely can allow sulfation to begin with means the plates are less likely to accept a full charge. Supposedly you can calculate "amp hours" against the cold cranking capacity of the battery, but I would just check it periodically with a hydrometer. You can get the really inexpensive kind with floating colored plastic pellets, or quite a nice, accurate, temperature compensated hydrometer from EZ Red for around $20
When I let one go completely dead, it takes 12 -18 hours, usually, at
6-10 amperes.At 2 amperes, it will take, more or less, proportionately longer.
This is very rough, but may help you.
Turn your charger up to the max, which you say is 10 amps. If you have a charger with a meter you might notice that the needle goes above 10 as it starts to charge and tapers off as it continues to charge. At full charge it tapers off to almost nothing, less than an amp in many cases. You need an independent means of testing the charge. You could measure the voltage and stop when it gets to 14-15V with the charger still on. Or you could disconnect the charger, drain the top charge off the battery by turning the lights on for 30 seconds, turning the lights off, and then checking the battery voltage. It should be about 12.6V. In a case like this with a suspected bad battery, various things can happen. It might sit on the charger forever and not come up to the standard I proposeed above. The charge rate might never come up. The voltage may never come up. It could appear to be fully charged and then when you hit it with a big load like cranking the car, the capacity might not be there. So be aware and don't run off and start looking for other car repairs until you make sure the battery is up to the job.
It should be about 12.6V.
All good points, Al.. Neither of us mentioned, as perhaps we should have done, that he should check the electrolyte level before he starts any of this. Many people don't realize that most batteries today can still be opened and checked for electrolyte level.
Family member had a battery go down completely recently. Apparently left the door open on the car. The battery cables were extremely corroded, so I took care of those. The battery also turned out to be low on water.
I tried to charge it on the 12 ampere scale, but it kept knocking the internal current protection offline. Seemed almost like a dead short.
After about a half day, it started taking a charge and finally came on up. I was very leery about this one but it has been working perfectly for a week or so now, and may be okay.
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