Audioguru is correct. Voltage inflexion is not a good choice for use in detecting EOC (end of charge point) for NIMH batteries. It works great for NI-CD, not NI-MH. To safely detect NI-MH end of charge, it is typically done by measuring delta temp/time. Problem is, NIMH is an exothermic charge reaction so the cells heat up during charging all the time, but they heat up at a faster rate when EOC is reached so you have to measure the time rate of change for temperature to catch the EOC point. Cell voltage might be used as a backup for temp detection, but I would not use it alone on NIMH.