Ok, great seeing this being done BUT, from my point of view…
Make sure you only use protected cells – cells with protection circuits built in, never cells un-protected. The light or charger may not have any protection.
Never mix and match… ideally at least buy how ever many you need from the one source at the same time… each batch of cells is logged for capacity and impedance (or should be)from the manufacturer. if not, not every cell(battery ) you buy will have the same initial capacity… Bit like what I have seen this week a 6400Mah battery was only 3000mAh.
Just saying its brilliant doing what your doing but be careful, the batteries side is always the least thought off and abused… but from first hand experience with my first company I worked at the factory burnt down from a single cell hearing aid battery that shorted out!
So please be careful.