Quote:
Originally Posted by David Inc.
Man! How dead are we talking?
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Any modern tender/charger (eg with more electronics inside than a fuse, transformer, couple of capacitors and a bridge rectifier) won't do anything at all with a battery that registers less than 2V. I presume the jump pack is doing something similar.
You can use a power source that just doesn't care - like a bench power supply - to get the voltage up, or hook up another battery in parallel to get the voltage up over 2V. Either just leave connected to charge the original battery until it reads over 2V, or jump/charge the combined batteries.
Automotive batteries are not designed for deep discharge; unlike the "old days", they could be suspect after this, or not really recoverable. I've had smaller AGM batteries charge for 36 hours, read fine on a voltmeter - and immediately fail when re-fitted. YMMV.