I found a deal on Tenergy 2600mAh 18650 batteries on Ebay. I have 9 good AW, CK, and Redilast 18650 batteries and a bunch of ****fire cheapo batteries. I heard some good things about Tenergy 2600mAh and decided to take a chance as they were only $14.95 for a 4 pack shipped from a dealer in the states. I didn't read up on what I was buying and 3 days later I got a 4 pack and found they were not protected and they were flat tops. One of the 4 was DOA but the other 3 were showing about 3.83 volts. I charged them up to 4.18 and dropped one in a single cell light to give it a try. The light is a Shingingbeam S-mini and rated at 2 hours 10 minutes on high mode for run time. At 2 hours and 15 minutes I hadn't noticed any drop in brightness and I turned the light off and measured the battery. To my surprise the battery still showed 3.53 volts.
I called the company and told them that I had one battery that was DOA and asked if they were having problems with these batteries. She said they were very popular and had very few complaints and would ship another out next day. I asked if they had any protected Tenergy batteries and she did for the same price so I ordered 4 of these and yesterday all five arrived in good shape. I have been running some run time tests in a couple of my single cell lights and all are performing well. I'm getting better run time than I have gotten from any of my batteries with the exception of the Redilast, AW and CK batteries. No they are not as good as those three brands but for only $3.75 each I'm not going to complain.
Only problem is they are flat top and won't work in my 2 cell lights.
Question. I have read that I shouldn't mix batteries in multiple cell lights but is there any problem in doing so other than poor performance as long as both batteries are charged to about the same voltage and they have similar capacity? I could use one of these batteries along with one of my button top batteries in my 2x cell lights. Thanks