DIYbanter - View Single Post - charging a fully discharged car lead acid battery

wrote:

The best option is to use the lowest current charger until you can
verify 10 volts on the battery unloaded after it sits a few minutes off
the charger. Then any higher current chrage should do fine. This is
only to provide a margin a safety on the excessive current draw the
battery is going to attempt to pull when completely dead. No sense
opening up the thermal fuse inside the transformer in your el-cheapo
battery charger.

I ended up borrowing a lab power supply and am charging it at 1 amp. I
figured it can't be healthy for the battery to take a high current
charge. From my experience in nickel batteries, fast charging shortened
battery life significantly. Not sure if this translates to lead acid.

I am suprised it actually reads zero volts, unless the battery has an
internal excessive discharge protect cutoff device. Disconnect the
battery and read the unloaded voltage.

You're right, I measured 0.0 at the cigarette light with the key in
accessory position. I guess they run a relay now to power accessories,
and there wasn't enough voltage to energize. The battery actually read
about 8.5 at the terminal, no load. I gave it 2 hours of 1 amp charge,
then disconnected it for the night. After sitting overnight, it reads
11.0 volts.

It's back on 1 amp charge again.