Hip Hop Slave Sabre

Yep I meant Li-Ion not polymer. something like a pair of 18650 cells would give 7.2V and plenty of capacity to power a small sheet for ages for about 90g, you just need an invertor to run off that voltage, or one to run of 3.6v and you could get the whole setup for under 100g and not have to worry about balancing cells for recharging.

Do you think you could get the inverter narrow enough to slide down the seatpost ?
I reckon I can, but like I say I would just be taking apart an inverter and reassembling it with a bit of chopping and soldering.