The APR18650M1A LiFePO4 batteries are high powered and low cost. They have a rated capacity of 1100 mAh, a rated voltage of 3.3V, and a rated current of 30A. 10 pieces cost $36 on eBay. I measured their internal resistance with the SKYRC B6AC V2 Charger.
I bought them because they’re lighter than the 1.3Ah 12V SLA battery used for the car horns on my bicycle, quite safe, and long life.
Possible applications of the batteries include battery pack rebuilding, power tools, flashlights, battery backups, and e-bikes. Note that they’re 3.3V which is lower than the 3.7V cells commonly used in electronics. They also need a charge voltage of 3.6V instead of 4.2V.
To test them, I installed them into a custom built 4 cell 18650 battery pack and connected it to the charger.
Compared to other LiFePO4 batteries bought from DealeXtreme, the APR18650M1A batteries have a low internal resistance. Those from DX have an internal resistance of about 0.18 ohm, or up to three times higher. If your applications are high current such as electric vehicles and power tools, you’ll need a lower internal resistance.
I have tested the batteries with a pair of car horns. With two horns, they should draw 10 amps which means the battery pack voltage drops to 10 to 11V. Unlike other 18650 batteries I used before, the horns didn’t click.
If you’re interested in a battery that’s lightweight, high powered, safe, and long lasting, I would recommend the APR18650M1A batteries or something similar.