Now I see how it works! Actually, my 2nd mod was on a light that has “similar” way of functioning, with mechanical side switch, like yours, and the driver above it.
Here is the thread if you want to take a look (second part of the post #1): My first mods! An experience, for sure!
Being more clear, now, how the light works what I think is that modding it with a good driver and good cells…would be a waste of time, maybe!
You can still do it, with a driver that fits that aluminium pill and that has a spring attached to make contact with the brass pin on the switch.
Also, if you use non high-drain cells, it will not give you much trouble with the mechanical side switch.
But still, the interface of the driver / switch / cells, needed to be worked carefully so that the light could function properly!
As I said, you can make it and it will be a nice experience, believe me!
But if you want a “reliable” flashlight, you will have better “stock” lights out there that will perform better and that will give you less trouble!
Still try to make that mod 
I started that way as well