Thanks for the opportunity to think again on the problem.

Your heat observation is not useful:

Charge of lithium chemistries sub-zero can be done by adding a heater
to the pack.

Pack protection circuits may use heat as a means to avoid overcharge;
by shunting overvoltage.

A third-party pack won't necessarily meet the specs.

A spare-part pack might be from a bad batch.

You could carefully disassemble the dead packs to analyse the pack
protection circuit, and scope the voltage and current over time to
find out how the charge chip or phone firmware works.

Trickle charge of lithium chemistries should not be done.  I'd be
surprised if it happens, but for products designed to fail it seems a
reasonable choice.

--=20
James Cameron
http://quozl.linux.org.au/
--=20
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