Low cost 18650 li ion cell which works fine. This is a chinese grade battery for low cost experiments and diy projects.
It is a single cell, compact and powerful battery cell with 2000 mAh capacity. It is very convenient to install in your project to fulfill 3.7 Volt requirement with high capacity.
The battery terminals can use in any compatible battery adapter/holder or it can be permanently soldered to your applications power source wires.