What type of rechargeable Li-ion battery is used in 636V2?

There are three 18650 button top Li-ion rechargeable 3.7VDC 2000mAh batteries pre-installed inside the unit.  

The primary chemical used in them are cobalt lithium manganese nickel oxide.

When it's time to replace the batteries, please replace them all at once, and use batteries that are 18650 button top Li-ion rechargeable format, that have 3.7VDC nominal voltage, and that have the same capacities, such as, they all have 2000mAh, or they all have 2500mAh, or they all have 3000mAh, etc., do not use different capacity batteries in the 636V2.