Futaba 3PDF FM Radio packs?
 

I am trying to make a replacement battery pack for my Futaba 3PDF radio. I was using reg. "AA" rechargable cells in the stock craddle, and It worked fine. Unfortunately, the craddle has broken, and is no longer useful.

I tried using the same cells that were in the craddle, and soldered them in an 8-cell sidexside pack. When i connect the new pack up...the radio says (LOW VOLTAGE) and is only reading about 8.9v.....but on the charger it charges up to around 12v!

I have tried this on two separate packs.....I am looking for some alternatives are some guidance!

Thank you