Update on this: I stacked two 2000mAh lipos, now it looks like it is pregnant. The stacked batteries are 1mm thicker than I anticipated. On the bright side, the battery life is improved a lot. It is around 8h (wired) now. I may try sanding down the plastic cover but two wide rubber bands hold it...
I picked up the biggest battery I could find here which is 3.7v 2000 mAh li-po and threw that into G5.
Its battery life is terrible now (around 2,5h) but I get to use it as a desktop, plugged into the PC USB. SQ is unaffected.
Here's what it looks like inside.
The battery looks easy to replace.
I believe it's a Li-Po battery but could be Li-ion too?
Any ideas, folks?
@Rja4000 @mike7877