The battery is an internal lithium ion. It can be charged via USB from
the computer or from the included power supply. No other batteries can
be used.
I just spoke with the Tekkeon people on the phone, they do make a mini-USB
adapter for their MyPowerAll battery (and are sending me one to try out).
It has issues with some cell phones that use a non-standard USB charging
mechanism, so it remains to be seen if it will work on the MicroTrack.
They also gave me the mAh ratings at various voltages for this battery,
which annoyingly are not in any of the manuels nor on the web site.
At 5V it should be good for 7200 mAh.
Jeff