Below is a picture of a battery shell for a NiMH circuit for a power assist wheelchair battery. I'm taking a guess that each of the 20 batteries is 1.2V because the entire circuit is 24V. These are rechargeable.

I'd like to convert this circuit to the same voltage (24V) and same capacity (3Ah). 

First, is this possible given the space you see in this wheelchair battery shell, and the circuit board in the pictures?

Second, what are the material requirements to be able to convert this circuit from NiMH to Li-Ion and the type of charger as well? What materials will I need to solder/weld the materials together, etc.. for the actual labor? I'm an electrical novice, so please ask me more questions (as comments) and I'll do my best to answer.

**Note: right click image and open in a new window to make it larger!**

![enter image description here](https://i.stack.imgur.com/4gJ8C.jpg)