While the Samsung batteries mentioned here (unprotected flat top, or protected button top) might be overkill for the PicoCalc since its power requirements will be more modest than a uConsole, they’d still be excellent choices. It seems like most 18650s seem to fall into a few categories:
- fake batteries that claim to have impossibly high mAH – not only will these not last long, they are likely to damage your hardwares since they might be so poorly made they could explode or catch fire.
- cheaper batteries that either don’t have very high mAH (and don’t claim to), which seem to be common at vape shops. These don’t work well (or at all) with the uConsole or Devterm since those devices require higher (and sometimes sustained) power draw which these sorts of batteries tend to struggle with. Something like this might work ok for the PicoCalc, and would probably be safe. They may need to be replaced sooner though.
- more expensive batteries that can supply higher power draw for longer periods of time, from trusted sources. One example is at the link below, but there are others. Generally speaking, Samsung and Panasonic seem to make quality batteries, but in all cases you should carefully look at the specs: not just the mAH, but also continuous discharge rate, protected (or not), discharge cutoff voltage, and physical length. For PicoCalc, most of that won’t be as important. Protected batteries with button tops just barely fit in the Devterm and uConsole. I’m guessing they’d fit in the PicoCalc as well, but haven’t tested yet. Originally, the conscensus on the forums seemed to be that protected was necessary for all the Clockwork devices, or at least was wise, just to be safe. But over time it sounded like all the devices actually have necessary protection hardware, so unprotected batteries were not really a risk, as long as they weren’t cheap trash/fake batteries. In any case, you should always be careful which direction you insert the 18650 batteries, and always store them safely so there’s no chance they will short out. While they might not explode or catch fire, you could still ruin them.
I don’t have much experience with this, long term, as I only started using these batteries with the Devterm and then uConsole starting a few years ago… But based on forum posts it sounds like cheaper batteries don’t tend to last as long, even if they do work for a while. I’ve had the same Samsung batteries in my Devterm for years now, and they are doing fine. So my gut feeling is that you get what you pay for. And considering how difficult it is to get Clockwork devices in a timely matter, I didn’t want to risk ruining mine. 