My design
My universal battery consists of dual li-ion cells to obtain an 8.4 volt battery, the same voltage used by most cameras.
Since I have always lacked a quick way to check the charged status of my camera batteries, I have included a small and cheap voltmeter module which can be activated using a small switch to see the current voltage in the battery.
For safety, I have also included a 5 Ampere fuse in the event of a short circuit.
I used a sturdy shrink tubing with glue to hold the whole unit together. On the outside of the shrink tubing, I glued a piece of velcro tape to have the ability to easily attach it to my camera stand or other surfaces nearby where the battery is used.