The background story
It’s winter again and freezing temps are taking a hard toll on the lithium polymer (aka lithium ion) battery in my mailbox notifier. You’d think the *not-so-cheap-anymore* lithium Ion/Polymer batteries you find on all the online electronics reseller should be fine even at -40C if hobby drones and electric cars like Teslas run on lithium batteries right? Wrong.
I used to have a MotionMote powered by a LiPo in my mailbox and I found that below a certain freezing point the LiPo battery would simply fail and need recharging, and it looks like there is irreversible damage to the cell due to the freezing temps (every cycle it dies it dies faster). Maybe this is an edge case but I don’t think I’m asking much of a LiPo battery to survive Michigan winter, I mean really – half the projects I can think of are outdoors. If you’re able to read through the chinglish datasheets for these LiPos, one thing that you can find is the low temperature operating point is somewhere around -20 to 0C (ex. here or here – look for “Working temperature” it will be -20 – 60C). So basically those are lies and misleading information, nothing unusual from our friends in china who love to sell us junk for what is now a trend of increased prices. These batteries from all US vendors are chinese and fail at between 20-30F (-4C). I bought several from different vendors to verify I don’t have a bad batch. They all fail. What I find intriguing is the guilty silence of the US resellers who promote these batteries. This is meant to break that silence or ignorance: chinese LiPos die in freezing temps!
Just think of all those kickstarters that use lipo batteries, here’s a photo camera that runs on Lipos and you will discover will likely fail when you take it on a fun in the snow day.
I trusted the datasheet and got burned, even sourced a larger batch of these batteries intending to offer along with the MotionMote kit and then realized they fail below freezing when the winter season arrives. I also found that USPS doesn’t ship batteries at all and there is a restriction of 2 batteries (larger than ~750mAh) with UPS and Fedex, a rule broken by at least one of the major US vendors that will I won’t name but I bet you are a customer of, it surprised me. I don’t know what’s the penalty if you get caught shipping more than allowed HAZMAT limits. So I gave up trying to arrange shipping for these cells and instead I will try to make my stuff with alternative power sources in mind, at least for the projects that make a lot of sense to be used outdoors. In fact I think all my projects that have lithium battery JST connectors also have adjacent pins to connect any other power source like AA battery holders if desired.
Of course LiPolys are prefectly fine indoors and will offer a high charge density per volume and are great for MotionMotes and other similar nodes; they are also very popular with hobbyists so I will continue to make boards that support them (boards with chargers), but I will probably never sell them knowing these limitations and given the difficult shipping restrictions.
Fixing my problem
As it turns out alkalines are pretty happy in freezing temps, and in the following post I will show the new upgrade iteration to my mailbox notifier, which not only replaces the battery but enhances it to make it into a weather monitor as well!