It does apply to LiPos (and there may be other exotic battery types that it applies to as well) but there are many commonly used rechargeable batteries that it does not apply to.
From my experience, I don't quite agree with this. I use NiMH batteries exclusively, and
there is also a problem if the cells in a series pack are not closely-matched. I'm sure that
most RC guys who sell the pre-made packs match NiMH batteries beforehand.http://www.promatchracing.com/whymatched.php
For my part, I simply buy packs of 4 NiMH batteries at a time at the department store,
namely standard brands like Kodak, Everyready, etc, and use them together, and it's very
common that one of these cells will start misbehaving after a while, and take much longer
to recharge in an individual charger than the others.
It's also happens that, if one cells in the series arrangement isn't quite up to par with the
others, then during driving loads, when the current is going through the cells in the opposite
direction to charging, the good cells can overwhelm the weak cell and discharge it, and
actually drive its cell voltage to zero, or even in reverse. I'm not alone in seeing this, it's
See also, http://en.wikipedia.org/wiki/Nickel%E2%80%93metal_hydride_battery
A complete discharge of a cell until it goes into polarity reversal can cause permanent damage to the cell. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one will be completely discharged before the others due to small differences in capacity among the cells. When this happens, the good cells will start to drive the discharged cell in reverse,
The weaker the cell, the faster this happens. 5 or 6 years ago, I build a jig that measured
individual cell voltages during load-driving, and could easily watch the weaker cells going flat.