Evan Monsma's Sony action camera died in 20 minutes. That is not a rounding error. The camera was designed as a stunt camera, prioritizing size and weight over endurance, but Monsma wanted it for general use. He built an external battery system from scratch to fix it.
The build has three physical layers. First, a CNC-machined aluminum half-cage bolts onto the camera body and adds mounting points, including a screw-mount for a neutral-density filter. Second, a 3D-printed mount clips a larger Sony 7.2V camera battery to the rig. Third, a voltage converter steps that 7.2V down to the 3.7V the original battery compartment expects, fed through a USB power adapter slotted directly into that compartment. No cutting, no soldering into the camera itself.
There is an unresolved problem: the camera overheats under continuous load, which prevented a real battery endurance test. Monsma believes the runtime is now practical, but he cannot prove it yet. That open question, plus the full mechanical and electrical detail in his video, is why you should read the original rather than stop here.
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