I am using Panasonic eneloop pro Ni-MH AA min 2500 mAh / 1.2 V (re-chargeable Batteries) using the Panasonic BQ-CC55 Charger for the Tonewood Amp.
When the Batteries are inserted, the closing shoe needs a bit of force to lock, after a few goes you will get the hang of it shutting (locked) without fear of causing
any damage. the Tonewood Amp is a robust and solid unit. I am overly impressed with the battery life, and the charger is one of the best I have by far.
Thanks so much, Shane! One thing I tell folks about replacing the battery door when there's a snug fit, is to line up the widest point at the bottom of the battery door into the slot it slides into on TWA itself before pressing down on the top of the batteries.
Another Battery to try is PaleBlue Lithium Ion Polymer rechargeable. I have gotten a steady 4.5 V at start of a three hr session with turning off voltage of 4.4. Recharge time is just under 2 hrs with built in mini USB port. Can be purchased on Amazon.