I am looking for some guidance regarding a project I am building. I am using a set of 6 300F 2.7V Ultra Cap cells with a balance board to create a 12V power supply. The purpose was just to experiment with them and I've also created a "boost pack" similar to some videos I've seen online. The amount of current available is enough to start a car. At this point I have two of these 12V (6 cell) cap banks in parallel. My question is, what is the safest way to integrate a rechargeable lithium ion battery pack into this project. My intention is to wire it in parallel with the capacitor banks in order to keep the caps charged while also offering longer lasting power source for charging a cell phone (I've wired in a usb plug). Before I integrate the battery pack I'd like to know how to do it safely and not set myself up for too much current flowing from the caps to the battery (not sure if that's an issue). The lithium ion battery pack is comprised of three cylinder cells and a protection board. Any recommendation for how to safely do this and how to safely charge the system?

 

The lithium ion battery pack is comprised of three cylinder cells and a protection board.

It's possible that's all you need but the devil is in the details. If that board can accept the voltage range from your capacitors and charger, and keep the cells charged properly, then you're all set.

You need a charging scheme that would work without the capacitors present. Then you need to limit the charging current when you add the capacitors. If they're all uncharged, they'll look like a short to your charger and you need to anticipate that worst case scenario.