environmental agencies have been attempting to discourage the use of NiCd, especially in



Europe. NiMH have been tried and tested in  Powertools for a number of

years but the results are mixed. Shorter cycle life compared to NiCd is the major

drawback.

The reasons for the relatively short life of NiMH are multi-fold. NiMH is less robust

than NiCd and has a cycle life expectancy that is half or one third that of the standard

NiCd. In addition, NiMH prefers a moderate discharge current of 0.5C or less. A  Powertools, on the other

hand, draws a discharge current of about 1.5A when transmitting at 4W of power. High

discharge loads shorten the life of the NiMH battery considerably.

NiCd has the advantage of maintaining a low and steady internal resistance throughout

most of its service life. Although low when new, NiMH increases the resistance with

advanced cycle count. A battery with high internal resistance causes the voltage to drop when a

load is applied. Even though energy may still be present, the battery cannot deliver the

high current flow required during transmit mode. This results in a drop in voltage, which

triggers the ‘low battery’ condition and the radio cuts off. This happens mostly during

transmission.

The Li-ion has been tested for use with Powertools but has not been able to provide the

ultimate answer. Higher replacement costs, restrictions posed by the safety circuit and

aging pose limitations on this battery system.

more info:http://www.abatteryweb.com/power-tools-battery.html