I have two suggestions. 1) purchase 3- 6V lead-acid batteries. Advantage - the original=20 charger might charge them just fine. Do keep an eye on the total=20 voltage while charging - terminate charge when the voltage gets to=20 about 22.5V total. That's (3 * 7.5V) - 7.5V is what I use for end of=20 charge condition when running 6V gel-cell batteries in Equalize mode. Little 6V 4AH gel-cell batteries go for cheap around here=20 (Edmonton). Check the wholesale Alarm Company supplier in your area=20 - ADI is a good start. 2) run the drill from 24V. Probably work just fine. dwayne At 06:03 PM 2/24/2013, veegee wrote: >Hi all, > >I have an old 18V battery powered drill which is missing its battery >pack. I'm pretty sure the motor is a DC brushed motor, judging by the >sparks and smell of ozone. I haven't opened it (or any other drill, for >that matter) up yet to determine the trigger-switch mechanism, but it >seems to be two-speed. > >Since battery packs are outrageously expensive, I'm thinking of using >two cheap 12V AGM lead-acid batteries in series to power this thing. >Very cheap, available anywhere, dead-simple maintenance, very high surge >current, decently sized. > >Question: is it okay to build a simple PWM motor controller and drive >this thing at 24V, with a reduced max duty cycle to prevent burning out >the motor? Since it's a simple DC brushless motor, I'm assuming that it >should be safe as long as the average power is kept below its max power >at 18V. --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .