/diy/ - Do It Yourself

>>1402219
>But how do I go about it?

already told you above >>1400647

get a transformer above 10Vdc, preferably around 12-15V, and put a current limiting power resistor in series with it. try various resistors while using ammeter to measure a current that's safe when the battery is all run-down. say 0.1 to 0.25A.