I am wanting to power a ATTINY85 with a small Li-ion battery or Cell battery holder.
Thanks for your message. The ATTINY85 is a 5V device (well, it will operate from 2.7 to 5V). With that said, the ATTINY85V will operate from 1.8V to 5V (note the V at the end of ATTINY85V)
Given the cell batteries are a nominal 3V, you could use pretty much any of them. Bear in mind they won’t “last” for long for high power use. So depending what else you are driving, you might want to use something with more capacity.
Here is my favorite holder. It has a handy built in switch. To get the best bang for buck out of that battery though, I’d recommend using a ATTINY85V so your micro stays online for the entire battery life.
If you are going down the LiPo path, then there are some details to consider. LiPo’s are very dangerous if discharged beyond 3V/cell. Also, they are dangerous if charged incorrectly or beyond 4.2V/cell.
You should use something such as a PowerBoost as it will provide a means to recharge your LiPo, and has a low voltage warning as well. Ideallly, your ATTINY85 should be monitoring the low voltage signal from the PowerBoost to safely “deal” with it in the event a human isn’t around to observe or act on the situation.