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is there a way to lower a transformers power from 25 volts to charge a 19.2 volt drill battery?

i got a 19.2 volt battery tool kit without the charger,and i have a 25 volt 2 amp transformer (110 volt input) im not using and i want to use it to charge the batterys if its possible. ive read online that 2 amps is not a problem but it needs to be the same volts and i have no idea how to knock off  5 or 6 volts i would apreciate any help.

Assuming this is a Nicad application, then the easiest way is to use a voltage regulator, wired as a current regulator. Nicads like constant current, not constant voltage charging. Use something like an LM350. I've attached a similar circuit used for an LED driver, change the values you need to suit what you want. The LM350 is pretty well a drop in replacement., but higher rated than a 317.

Be careful, the difference in supply/requirements appears as heat in the regulator
LED driver.JPG