On Sat, 18 Sep 2010 16:08:13 +0100, "Brian Gaff"
wrote:

I thought batteries used in these packs had to be matched to avoid problems
with reverse charging etc that might cause them to explode.

Matched - No. Assuming you install them with the correct polarity and
the protection module is functioning correctly, the explosion risks
are from another category. There is also a connection sequence for
attaching the module to the series-connected cells. IIRC it starts at
the most positive terminal and progresses to the negative end last.

But matching IS important in that the protection module monitors cell
voltage DIFFERENCES. This has a two-fold effect. If the diffences
exceed a certain threshold value, the pack will be disabled by the
module. Below that threshold value, end-of-charge voltage will be
determined by the highest cell voltage (which leaves the others less
than fully charged) while end-of-discharge is conversely determined by
the lowest cell voltage. So as the differential increases the usable
capacity reduces in the interests of safety.