Looking for external battery options. My knowledge the subject is limited as I've used the same 4 "dvd" batterys for years for my old V3 and r44.
Cage uses a Tek 3450. First they are not widely available and there are lots of bad reviews! Hell one about charger catching the battery on fire here on ts! I've read about the Naztech PB15000 but they don't seem to be available either.
Anyway power requirements for the femto are:
Powering: 2 x 9V batteries (type 6LR61) or external (12-18V)
The low voltage threshold is set to 13.5V (2 x 6.75V).
12-18v / 4-pin Hirose Male connector / pin 4 for (+) pin 1 for (-)
Small and light a plus!