Originally Posted by
Rodney
I hate to disagree with John as he is most always correct but I have found that it is safe to drop down to 1.1 volt per cell if using Nixx type cells; they still have about 5 to 10% of their energy at that voltage. Of course discretion is the better part of valor though so it does not hurt to be a bit on the conservative side.
And 1.1 volts per cell is still 5.5 volts or well above the 4.2 the OP was asking about. Either way, that is getting very close to being completely discharged as 1.1 v is considered fully discharged for testing purposes. When using these batteries, I was much more conservative than that and for a 5 cell pack, 6 volts seemed like a good place to stop and recharge.
Like pilotpete2 though, I've pretty much changed everything but a few transmitters over to A123 LiFe batteries these days so the Nixx info is becoming a distant memory.