Charging curve of charger for NIMH battery pack

The charger for NIMH or NICD battery-pack also need to monitors the cell's temperature and voltage when the series number big than 10s. When cells pack reaches full charge, the temperature monitor enables another termination technique. Termination on this positive temperature slope is called DT termination, see above white line. Other factors that can trigger termination include charging time and maximum cell voltage are assistant conditions. Well-designed chargers rely on a combination of these factors. 
 

Here giving a real curve from N100-24 charger, tested with 8Ah 24V NIMH battery pack.

NIMH charging curve (Yellow-Voltage, Pink-Current, white-Temperature)

 

Note: Because certain effects that appear when a cell first begins charging can imitate termination conditions, chargers usually introduce a delay of one to 5~15 minutes before activating slope-detection termination modes. Also, charge-termination conditions are difficult to detect for rates below 0.1C, because the voltage and temperature slopes of interest (DV/Dt and DT/Dt) are small and comparable to other system effects.