Thanks for the props, fmerkel.
For the record, I absolutely do not consider myself an expert on these things. But, I do know enough to feel like my Opus charger/tester (which I do recommend to anyone as a good 4-battery charger) is giving me reasonably accurate and useful info.
And it is my understanding (not being an expert) that fmerkel is exactly correct. Dive lights like these definitely do not need a high drain battery.
And,
@Jondjames, to directly answer your question: Yes, a higher mAh battery will keep the light on for longer. But, as has been noted, you can't judge a battery's capacity by the rating on the label. To last longer, it needs to actually BE higher mAh capacity, not just say it is on the label.
Related to that, I will point out that if you're going to have rechargeable batteries, you need a charger. As with the batteries, chargers range from cheap single-cell chargers that are practically worthless, to multi-cell chargers and even testers.
I have enough lights, strobes, etc. that I have a 4-cell tester/charger now and I think I'm going to buy another one. Some days, being able to only charge 4 batteries (or 2 x 26650) at a time is very inconvenient. Anyway.... if you're going to invest in a decent charger, you may as well buy once, cry once, as they say, and get a 4-cell charger that also has a decent Refresh program and the ability to test cells.
I have used my Opus to test cells that tested very low, compared to their original capacity, and then used the Refresh program to restore them to very close to their original capacity.
And, even good quality batteries go bad eventually. Being able to test your good batteries periodically, so that you can know when it's time to replace them could easily save a dive for you.
So, if you're going to invest in rechargeable batteries for dive lights, I definitely would suggest to consider getting something like the Opus BT-C3400 to charge/maintain/test your batteries. $55 or so is not THAT expensive for what you are getting.
https://www.amazon.com/BT-C3400-Universal-Analyzer-rechargeable-batteries/dp/B00NR77SL2/ref=sr_1_1
Just for the record, you can use this unit with 4 different types of batteries in it and have each one on a different program (i.e. 1 on Charge, 1 on Refresh, 1 on Discharge/Test, 1 on Discharge) simultaneously. And it has options for how much current to use when charging or discharging, from 500mA to 2000mA. So, if you're in a hurry, you can bump it up to charge at 2A. Or if you have all night, you can let it go at 500mA (which I think is better for battery life in the long term).