The data below illustrates why. This data was collected using a 15 cell 4 Ah battery, being charged at a c/15 trickle rate. Note how the battery reached a maximum temperature of 60 degrees C, even at this low charge rate. This data is a perfect example of why controlled charging is required when using nickel metal hydride chemistry. Prolonged exposure at elevated temperature is detrimental to cycle life and should be avoided.

Note: E.D.S. has deliberately posted data that illustrates the dramatic effect of NiMH heating. The actual heating will vary by the number of cells and particularly Ah rating. If you are considering using a constant current charger with overcharge protection, E.D.S. will gladly test and provide temperature data so our client and the battery supplier can make an informed decision.