Samsung 30Q button top are good general batteries. They are also easy to find and pretty cheap. Here is a link to a sale for them. 4 button top for $16 plus couple dollars for shipping. I just bought these myself. Use the code when ordering to get the discount.
You don’t need an expensive charger. Some good ones are the Liitokala Lii-500 and Zanflare C4 (which are both 1 amp x 4). Both can be found for $20-$25 with coupons.
I would not get the VC4 as it is quite slow ((0.5 amp x 4). The Opus is a bit tricky. Some versions have noisy fans, etc…
You should always stay close to the batteries when charging for safety. They can be left in the charger, but try not to leave them in there overnight or unattended.
When using 4 batteries in this light make sure they are always at the same voltage before installing them. It’s best to fully charge them so you know they are all at the same voltage.