custom battery packs for 70D

[Davey]

I wonder if anyone has tried this, details to follow. I want something to give me more runtime for less space in lightweight loadout. This isn't meant as substitute for a spare battery as that is always good move. More like long runtime with no cell change and take up less space than setup of multi batteries and a grip.

I have a mains power adapter for 70D and have used it in a pinch plugged into a portable inverter I use for monoblock outdoors recently which is where the idea came from. Obviously this isn't great combo as the inverter is bigger than I'd like and overkill for this purpose. I have a ton of decent 18650s and cradles lying around and thought if I wired it into the fake battery part of the mains adapter it'd work but this isn't something I know a lot about. I asked a friend who is an electrical engineer and he thought it'd work but admits maybe something he hasn't considered. I've made a 2s2p pack to try it but not plugged it into my camera to test it and thought I'd ask for similar experiences or idea from people likely to know more hence asking here.

Issue I have is input voltage since fully charged cells terminate at 4.2v taking 2s to 8.4v ish. The regular canon battery claims 7.2v so I presume it is 2S cell and probably terminates at similar level. The mains adapter says 8v output so I guess the camera can take it but don't know. As for current that many cells in parallel will give it what it needs without problems. If it does work I'd think about modding to 2s3p or even 2s4p for hell of a runtime in small package. Any thoughts or ideas greatly appreciated.

[Davey]

just answered my own question, did few tests today metering the normal battery at various levels, DIY pack and mains adapter then decided to test it based on results, it seemed fine and works a charm. For those who may try similar I may adjust my charger to terminate at cells 4.15v ish rather than 4.2v to be on safe side since the canon battery is 8.2ish hot off the charger at 100% where my pack is 8.4v for short while.

The 3100mAh cells in 2s2p should be more than long enough for high video use and live view shooting as well as long hours outdoors on cold nights. Taken it to bits again now I know it works as going to use better quality bits like nice cradles, good connectors, better cable size and put it in project box maybe and shrink wrap bits etc so it is more like a commercial solution although I am yet to see this surprisingly especially for video or long sessions in cold.