If it is too good to be true …….
I’ve tried a number of the off-brand 18650 batteries. While I don’t own test equipment needed to do a precise test on the discharge characteristics of the batteries, one simple way is to first weigh the battery and then use it fully charged in a light, measuring the time it takes to have the light indicate it needs recharging. What I found is that the higher the rating on the label, the lighter the battery was and the shorter the discharge time. That makes sense when it comes to weight. If the battery has less electrolyte in the case, it can’t possibly have a higher capacity. You can’t make a 9900 mAh battery in the first place and certainly not make a good battery for 75 cents each. It’s like the ratings for flashlights. The CREE XML-T6 has a maximum output around 1050 lumens (so says CREE) but I see T-6 flashlights rated at 10,000 lumens on eBay. It’s pure fiction.
The results (from memory):
“5800 mAh labeled” Ran 2.5 hours and weighed 27 gams
“4000 mAh labeled” Ran 3.5 hours and weighed 35 gams
Genuine Panasonic battery 3,400 mAh Ran 16 hours and weighed 75 gams. This is one of the highest rated batteries by every source I could find. I paid around $14 a pair including postage. The other two “Trustfire” batteries were around $3 including shipping. They work fine for non-essential uses like powering DIY LED bike lights but for my flashlight I used the Panasonic batteries.