I haven’t taken this one apart, but it’s too thin to accomodate 18650s. I think it’s just a rectangular pack. I will probably take it apart just to see if I can salvage any of the components but I haven’t gotten around to it yet.

My immediate concern is just charging my phone when I’m out and about, and for that I don’t need passthrough or hotswapping or any of that stuff. If I have my Pi out in the field and I’m running a test, that’s when I’d like things like passthrough or hotswapping so I can leave it out there for days at a time and not have to reboot it.

The hot swapping specifically is a long term ambition I have for some farm rovers. I want to do moisture sampling and maybe even some surveillance of weeds / insects with some cameras mounted to them, and then generate some reports based on the collected data. The idea is I’ll have different units that do different things, and have different power requirements, but they all run on interchangeable cells that can be recycled through the same charger. It’s extremely not necessary and it’s definitely easier to just reboot the device once the new cells are installed, but I like the idea of keeping the on-unit compute active so I can see analytics from its perspective throughout the process. The Pi is overkill for what I’m doing, but those are the boards I have at the moment (those, and all my old android phones) so that’s what I’m using to prototype. If I ever build something that I want to scale, that’s when I’ll start thinking about optimizing compute for the task I’m building for.

The pass through would be for something that doesn’t offload the cells, but rather docks into a station kinda like a roomba does. I’d just hook the charger up to some contact plates and have it park on them (or set the rover in the dock myself), and the rover would be able to undock itself and get to work once it’s charged. I’d still like those to use replaceable cells, just so I don’t have to desolder anything when the cells start to fail. I’m planning to prototype both, which one ends up being easier depends a lot on what hardware I can buy vs. what I have to cobble together myself.

I’ll read up on those. I want to have a trickle charger attached to my main power anyway for the known-good batteries in my array to keep them from discharging too far in low production times, so if they hold a charge they’ll probably live on one permanently

good note, I’ll keep a lookout for that.

A few of them are sealed, some have pop tops. The few I have opened are completely dry. My plan for the ones with removable caps I’m planning to fill with distilled water and test, then try to recondition them with a desulfator and see if I can detect any difference. never reconditioned batteries before so it’s going to be a learning process. Not sure what, if anything, I can do with the sealed ones, I’m focusing on the ones with caps first.