Where does one find a powerbank to dimensions? I want it to be comfortably fit at the base/bottom of my top tube bag, take all the available horizontal space, but stay thin so I still have plenty of room left. 10,000 mAh should be OK. The area dimensions are roughly 225 x 45mm (45 can stretch a little bit, 225 is max and including plugs etc) and I want it to be no more than 10 mm in height... It's not a common dimension, most products are either too wide or too thick.
Did anybody DIY a "link-sausage form factor" powerbank before and put it inside the downtube? Just get a few cells that fit the bill (CR123A?) and shrinkwrap them, connect them (series/parallel/separately) like sausage links and insert them in the downtube from the BB side, or if possible into the top tube from the headset side? Not sure about where to put the dis/charging circuitry though.
I just want onboard GoPro footage without the hassle of changing batteries and/or missing footage due to forgetting to check power and/or recording status. Maybe a GoPro remote on the handlebars could be easier? Not sure and I'd still need to charge/change for power.