LiPo (Lithium Polymere) batteries are interesting batteries for IoT as they are nt so much expensive, easy to get with multiple form factors and multiple capacities. As they are used for radioguided planes and such toys, you have a lot of really small batteries available for a couple of euros.
The Lipo battery is typically providing 3.7V. This sounds good for 3.3V circuit. The charging circuit is quite easy and low expensive compare to some others battery technology.
But there is no miracle and a couple of problem I’m actually discovering and this post will introduce.