Honestly, when will there be a battery upgrade? Replacing these AA batteries has certainly proven to be a pain in the butt. Some design modifications to support a 5 volt, cell phone-style battery are in order. Make it USB rechargeable and replaceable.
No immediate plans, but the input is greatly appreciated!
For the time being, try Tenavolts brand rechargeable batteries. We're getting 12 hours playing time per set, per charge, and they charge in about two hours.
To be honest, I can't understand the problems some people complain about regarding batteries and the TWA.
Over the last few years there have been been several discussions regarding batteries.
Personally I've been using Eneloop Rechargeables wherever possible for years now, and started using them with the TWA basically from day one. My experience is that they function very well for me with a good 3-4 hours per charge. I Have 2 sets of 3 which means that I'm basically covered for at least 6 hours of playing which I've never run to the end of in any particular session. Were that the case I'd buy a third set.
I'm happy that I'm able to use perfectly "normal" types of battery. The way the batteries fit in the TWA means that it doesn't have to be monstrous in size.
If the TWA had been constructed as Duane Woody suggests, I'd be unhappy, but would live with it because I knew what I was buying in the first place. A cellphone-style battery would also only have a certain amount of charge, and then you'd either have to have one in reserve (expensive compared to Eneloop AA rechargeables), or then be forced to have a break until the batterie is charged up again.
My suggestion is to buy good rechargeables (Eneloop AA's are available with ca. 2500mAh capacity) + an intelligent charger plus a second set in reserve). They're good for at least 500 recharging cycles and have a very small capacity drain.
Has this been of any help?