Thanks for posting the solution!It's been a long time since I visited this forum. More than 5 years are passed since I asked a question here.
For anybody interested in a solution, here is an answer: the way to detect Alkaline batteries in charger is monitoring its charging curve (constant current charge) during first few minutes. Even with a low charging current applied, the voltage on Alkaline battery will rise to its initial value (mature cells), while Ni-MH cell' charging curve will rise very slow (almost unchangeable during first 2-3 minutes with a low charging current). Then, if the voltage is raised immediately, the charging process should be terminated. Otherwise, the charging battery is probably Ni-MH. Low current for few minutes into Alkaline battery shouldn't damage it (i.e. the battery wouldn't leak). Of course, such a charger should be controlled by uCU (or very complicated discreet HW).