I've been searching for ways to expand the battery life of my old Sony A7s II DSLR and the best I can think of would be to build a custom battery using bigger LiPo cells. There are two 3.7V small cells inside a the original camera battery NP-FW50. What about desoldering those and replacing them with bigger cells to the same circuit?
video sample from: https://www.youtube.com/watch?v=l5tpniji5Eg
I can imagine wiring up a pair of 5000mAh to the actual battery circuit and racking it under the camera. One of those hard case made for toy cars have a good large size/format, quite similar to the size under the camera. They are also made of two 3.7v LiPo cells in series.
Would there be any electrical counter-indication to do this? I ignore what the battery PCB does exactly, apart from voltage regulation and charge protection. Which internal restrictions might bring the experiment to fail.
Charging might be also an issue since the Sony charger (8.4V) is only 0.28A –almost 18hours to charge 5000mAh. But that's another issue.