keep in mind if you buy a charger and want to charge the OEM battery with it that that battery is almost 1/4" longer than standard, so you'd want to make sure the charger will accommodate that extra length. Not that that battery is likely so good that you'd want to buy a charger specifically for it...
I will measure how much energy the battery can deliver when I have a chance. Not holding my breath that it's close to 2.2 Ah, though, based on previous experience with generic chinese batteries.
Btw, talking about inflated specs, I saw some similar but no-name lights on
ebay advertised at 10,000 and even 80,000 lumens... And for like $6 too... Potent!
Added: I tried to check the discharge cutoff voltage. Best I could tell without opening things up is that the light turned itself off at about 3V. (I measured 3.05V 5 secs or so after turn off and it seemed to increase by about 0.01V a sec or so after that. Very rough of course, but seems like a clean level that a designer might want to use for aesthetics so I can buy that.)
So, it appears that the circuit is limited at 4.2V max and 3.0V min. These values seem safe (from memory) for standard cobalt-type Lithium ion batteries. Somebody correct me on that if wrong, please. The 4.2V is as high as you'd want to go I think to be safe and get highest capacity per cycle, but is not the best for longevity in number of cycles achievable.
But this suggests to me that the circuit is reasonable at least and can probably be used without too much risk for your better batteries (of standard composition).