Thanks. I tried to connect NimH rc battery pack 7.2v 4500mAh with pins inside the battery, just beneath the big capacitor.

For reference, I took the below reference.

I did not resolder anything like as shown in the above link.

Note: Positive is common for both alkali and NimH and Negative is close to positive for NimH and far for the alkali.

It works great. At full-manual the recycle time is just below 5 seconds.