NiMH vs NiCd Batteries under High Charging Rates

In last years, NiCd and NiMH technologies have settled in the market of medium/high capacity batteries. Fast-charge is very interesting in different applications (communications systems, electric vehicles, low-earth-orbit spacecrafts) in order to minimizing charge time. The problem is that high currents involved in fast-charge process affect battery behavior modifying parameters as battery charge acceptance. Moreover, battery temperature increase and gasses production related to overcharging make necessary to detect accurately the end of fast-charge to avoid battery damage. Limited information about results of charging process at different charging rates (i.e. time reduction versus charge efficiency) makes difficult to select the optimum rate in each specific application. The lack of information is more problematic in NiMH batteries due to they can not support as well as NiCd batteries extreme working conditions. For these reasons, an intensive study about NiCd and NiMH battery behavior under different charging rates was developed. In this paper, the effects of fast-charging on medium/high capacity NiCd and NiMH batteries are shown. In this way, conclusions about the application range of fast-charging in both technologies are drawn