As a follow up, I also tried:
Olight 18650 Protected for high drain devices (3600mAh, 12.9w, 3.6v)
Fits DevTerm just fine (easier to insert than Nitecore NL1823). Still need to perform reliability tests, but it seems to be charging just fine for now.
As another follow up, I can also confirm the following:
KeepPower 18650 Sanyo Protected (3500mAh, 10A, 3.7V)
Fits DevTerm just fine (easier to insert than Nitecore NL1823). Still need to perform reliability tests. Still trying to verify if battery will charge, but i see no reason why it wouldn’t.
These fit nicely in the battery holder. They’re easy to remove. The battery door fits over them perfectly.
They provide about four hours of fairly continuous use. They appear to be unprotected. They come with a plastic storage box that snaps closed.
any updates on reliability
I got these too (KeepPower 10A 3500mAh - 18650 Battery (Protected Button Top)) and they fit perfectly, no bulging compartment and they are pretty easy to take in and out. They also charge perfectly well within the DevTerm.
Not had mine long to comment on reliability but they are working very well so far.
Trying to guess the power draw:
I’m not good at battery math, and trying to figure the following DevTerm and uConsole use case out: so the Pi 5 will apparently draw up to 12W, and I heard the average SSD plugged in via USB will also draw around 8-10W peak. I would like to be able to use SSDs under all circumstances. Edit: I forgot the modem which mine will have, which i guess can draw up to 10W too (we’re looking at max. peak which this post suggests the modem can reach, not average), and the screen I guess. Edit 2: found numbers for the screen, apparently slightly above 4W for maximum brightness.
Trying to guess the total power budget:
So what, does this put me at some battery that supports something around like, past 35W discharge, does anybody know? That does feel a little high. Edit 3: this post suggests a 30% safety margin, and with all of this I guess we end up at:
I guess that does match the beefier Raspberry Pi 5 45W power supply, but still feels like a lot, so I’m wondering if that’s true? Even the Steam Deck with SSD will apparently draw less than 20W under full load when not charging, so that’s why I’m wondering.
Trying to guess what batteries might work:
Now most batteries have their Continuous Discharge Rating specified in A, not W. Do I multiply that with 3.6V, or with 2.5V (lowest voltage allowed for most of them), or with 5V to get how much Watt they’re rated for without overheating? And then since it’s two cells, is it enough if that covers around 22.5W plus some headroom, or do both need to support 45W minimum? For now, I’ll assume both cells need to meet the rating and that it’s multiplied with 2.5V.
For my use case if we’re assuming 45W is actually true, that makes me wonder if I’d be looking at 20A batteries like the Samsung INR18650-20S with 2.5V * 20A = 50W, if that makes any sense at all. And not the Samsung INR18650-30Q 15A or 35E 10A then, but what do I know. Any input appreciated.
Call for help:
Sorry if this is a silly question, I’m not used to doing this math myself. Can anybody more knowledgeable tell if the ballpark looks correct for my uninformed napkin math? Since the DevTerm and uConsole have both a BMS, I might consider unprotected cells, but I assume they still need to be rated correctly to avoid a fire hazard. And I’d rather be on the safe side.
I got some updates on the battery situation:
As a result, it seems like one could assume anything beyond a 15A Continuous Discharge Rated cell is probably wildly unnecessary. (Assuming the cell is legit and not fake rated.) Not that I know for sure.
Disclaimer: everything I say could be wrong, I’m not a qualified electrician.
Hi all, n00b here. I’ve just received a PicoCalc Pico-H here in the UK, but I’ve no idea what batteries to get as there seem to be a lot of wildly different specs.
Can anyone point me at something worth buying?
any 18650 of capacity 3000 – 3500 mAh
even the cheapest and the fakest one should work okay in picocalc
Thank you! I’ve seen a lot of talk about the physical size - some people say that anything over 69mm in length may or may not fit. Is that something I can ignore too?
I don’t want to appear rude, but the battery topic has already been discussed in detail several times.
Please use the search function.
I understand. I did actually search for this, and have spent several hours reading a few different threads: but, like most forums, they are full of contradictory posts, people claiming one thing is perfect and others saying it’ll blow your machine up, and lots of people saying to search and research things.
What is noticeably absent, is a single post that lists the specific parameters required, and maybe a recommendation of a specific cell that has been proven to work correctly.
Do you remember what it’s like to have the choice of flat top, button top, or middle top? Of 3.5v, 3.6v, 3.7v? Of 68.50mm or 69.80mm length? Protected or not? 2200mAh, 3000mAh, 3600mAh? 10A continuous discharge or 5A? Etc.
I couldn’t find a single post that clarified all that in an easy to read list by searching, which really is true for most forums on the Internet.
The problem is that everyone has different preferences and must decide for themselves what is important to them.
The most important criteria are capacity, safety, quality and price.
Basically, the designation 18650 refers to the physical size of the cell: 18 mm in diameter and 65 mm in length. Deviations from this are mainly due to optional integrated protective electronics.
The higher the capacity (mAh), the longer the device will run on one battery charge. It should be noted here that the highest reputable capacity achievable is 3,500 mAh.
There are cells with and without integrated protective electronics. These often protect against overcharging and undercharging, reverse polarity or short circuits. However, what protective electronics actually cover can vary, and you must refer to the manufacturer’s specifications.
Speaking of manufacturers: batteries are a matter of trust. It is worth relying on well-known and reputable manufacturers, as well as trustworthy suppliers.
Most batteries with protective electronics have a raised positive terminal. The battery holders in clockwork devices can accommodate both raised and flat positive terminals. Some users trust their ability to insert the batteries the right way round and the device’s own charging electronics, while others insist on having batteries with integrated protective electronics.
Many members of the forum use SAMSUNG 35E cells (a recommendation that is often found in this forum), at least in the uConsole. However, the PicoCalc has lower maximum current requirements than the uConsole and will probably run properly even with weaker cells.
Therefore, even this new post can only list the possibilities without making a definitive, final statement about which battery is the ‘right’ one. This decision is up to each individual.
There are also a few specific PicoCalc related issues that are buried on the forum.
For instance, if you want to use two cells, you should ideally have them fully charged when inserted, since having them be at different charge levels may not be advisable, as mentioned here:
If you’re only using one cell then this isn’t an issue.
There was also some discussion about overcharaging on PicoCalc, which seemed to be a flaw in the design. My interpretation of it was another reason why it would be a bad idea to use cheap or untrusted batteries in the PicoCalc, and may also be a good reason to choose protected cells over unprotected ones.
I’m using the protected Samsung 35Es myself (two in the PicoCalc) because I had already bought them for the DevTerm and uConsole in the past, from a reliable supplier online. While they are probably overkill in terms of quality and capacity for the PicoCalc, they’re also arguably some of the safest to use. The extra length makes them a tight fit, but I don’t plan on swapping them out until they die, which may outlast the PicoCalc’s life itself.
While it can be avoided with some care, if you choose unprotected, and put them in wrong, then you’ll likely damage the batteries and the PicoCalc, as described here. And the cheaper and “sketchier” the batteries you use, the more likely this will happen too. Even if they are inserted correctly, if they are fake/damaged batteries that could happen. In general, anything advertising capacity over 3500 could be a fake and shouldn’t be trusted.
BTW, this battery discussion post is tagged on the DevTerm forum. But I guess it doesn’t matter much these days since the DevTerm has been end of life for a while, and activity had dropped to nothing anyway. It’s just that other PicoCalc users with battery questions may not find it as easily since it’s here. 
I was so bold as to change the tag. Because you’re right, the topic is now relevant for several types of devices.
This was overblown. The charging IC used by the PicoCalc actively prevents reverse current flow between the Pico and the battery. I’ve also tested this empirically and have not been able to see any incorrect voltages presented to the battery, regardless of what power is supplied to the pico’s USB port.
This part of the design is not flawed, only the analysis was.
Thank you for verifying that personally. That is valuable information.
Thank you all for contributing to this thread: I’m learning by the day, and there seems to be a lot of exceptionally useful information here.
Can I ask if anyone knows if 69.0mm is the actual maximum length that will fit in a PicoCalc? I don’t know if a 69.90mm battery will fit or not.
Also, I’d ask if the supply voltage matters at all? I’ve seen them at 3.5v, up to about 3.75v, and I don’t know if any of them are ‘bad’, or it really doesn’t matter.
These are the most pressing questions I have on this, so if I can get a simple answer, maybe we could make a pinned post listing these details?
The requirement for identical charge levels if two batteries are used may be a life-saver - thank you!
I don’t have a separate charger for 18650’s, so would it make sense for me to put one battery at a time in the PicoCalc, let it charge up to full there, and then swap it for another, just to be sure I have equal charge?
Charging them one by one, in the PicoCalc itself should be fine. Several firmware support a query for battery percentage. The PicoCalc Text Starter project by @BlairLeduc makes it easy with the “battery” command, but it can also be done in newer versions of PicoMite and some other firmware.