DIY battery charger from old cordless power tools?

I was just thinking what would feasibility be to take some old cordless power tool battery chargers and modify them to be used for charging 7.2 v(nominal) Prius battery modules. Would probably need some modification of regulator circuit to set maximum voltage and current. The older ones from 9 to 12 volt tools can often be had for nothing. I'll have to dig out an old one and experiment. Has anyone else done so already? It might be a cheap way to charge multiple modules at once.