I built a test box that is required to run on a 9 volt nimh rechargeable battery. The battery is intended to remain inside the box and recharges via power jack(2x6mm) on the outside of the box. The energizer recommended charger is not financially feasible and the design of the box requires a standard ac/dc plug in transformer to charge the internal battery...my problem...the energizer charger charges a 9 volt battery at 30ma for about 8 hours and also includes circuitry for overcharging, if i dont have the energizer charger and want to use a standard wall ac/dc transformer how do i properly use a 110~220 input 9 volt 30ma output transformer?? Where can i find one?? Are there any better ways to charge the battery?? Please advise

 

Put NiMH charger in Find box, upper right, this page.
Would help to know capacity of battery-7-AAs or 7- AAAs??

 

Its a 9 volt Enerigizer Recharge 175 mAh

 

When referring to batteries the chemistry they use is critical. Each has its own quirks, and requires different circuits to charge them correctly. Most batteries have it written on the case, if they are meant to be recharged.

The Battery University - good reference.

 

An Energizer "9V" 175mAh Ni-MH battery has 7 cells. When fully charged it is 9.8V to 10.5V. After is has discharged a little its voltage is 8.4V.

Energizer says that a Ni-MH battery should not have a continuous trickle charge unless its current is limited to 1/40th its mAh rating which is 175/40= 4.4mA.

30mA is too high a charging current. The 175mAh battery should be charged at 17.5mA for 14 hours then the charging circuit should turn off or reduce the current to 4.4mA.