Best practice for using lithium as backup power for an always-on project?

Projects General Guidance
1

Hi, I have a project that's powered by a wall wart that I'd like to keep powered during outages/survive being unplugged for up to a few hours. I have tons of 18650 batteries from my vaping days that I like to use in my portable projects. This time I'd like to put a cell or two to work inside a box with a critical purpose that must remain powered at all times.

As I understand it, one mustn't leave lithiums in a constant charge state as the risk involves damage to the cells/potential fire. How would I go about safely setting up 18650 cells for use as a UPS for a small project that only draws a few mAh?

Thanks for any advice.

2

You can go on eBay and get the boards that control charge and behave as a UPS for your project. Use this "ups li" as your search term it will give you lots of hits for less then $5.00. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

3

Do you need to do anything while you are disconnected, or do you just need to store something and keep the time alive? Some microcontrollers have special backup memories with a real-time clock that can stay alive when you connect a coin cell to some special pins.