[Shop-talk] Recharging a Ni-Cad Battery

[Karl Vacek]

> Also, NiCads, unlike many other batteries, have no issue and may benefit 
> from a very occassional, full and complete discharge.
>
> Jack


This is a little off from Eric's dive light question, but...

As an R/C pilot you can't mean that.  You have a potentially lethal weapon, 
and an investment of hundreds (or thousands) of dollars flying around 
completely dependent upon the health of your radio batteries.

If you're referring to completely discharging a nicad back as opposed to one 
individual cell, DO NOT do it.

Maybe one or two complete discharges won't do any noticeable harm, but more 
than a few will begin to destroy the weakest cell in the pack.  As the cells 
discharge, one reaches 0 volts first, and the current from the others 
flowing through it as they continue to discharge will reverse-charge that 
weakest cell, reversing its polarity.  Then the second-weakest cell will 
reach 0 volts and reverse polarity, and so forth, till only one cell is left 
with any voltage.

Do that a few times and you've ruined one or more cells and thus ruined the 
pack.  That's why there are smart chargers and dischargers and 
expanded-scale voltmeters to monitor the state of charge and discharge of 
nicad cells and battery packs and exercise them as well.

Karl