Disclaimer, if you don't know how to "nicely hack" don't attempt the following.
I decided to increase the battery capacity of my Glo, opened it, measured the space between back cover and board, looked around for a battery with suitable dimensions, spliced the new battery's wires to existing battery wires, and... voila... theoretically doubled the capacity of my Glo, in reality not so due to batteries aging.
This is the last mod I do to my Glo, its about time to replace it with something bigger for bigger fonts, do away with +1 glasses, and sharper text.
See link below for accurate information about batteries.
https://batteryuniversity.com