Hello, no idea what you mean by 4S or 8S.
Please be more specific the type, and capacity battery.
Many dedicated IC s exist for battery charging.
Do not use an LED drive, completely different.
You do not mention the power source, 240v mains?
Finally beware that lithium batteries are potentially dangerous and catch fire or even explode if improperly charged.
There is a safety, compliance and liability issue in such a project especially if intended for volume manufacture.
As the cinéma and still film portable lighting market is well developed, you should survive the available lights and battery packs and chargers already existing.
Just the rambling of an old retired EE!
Bon Chance
Jon