The battery is the LP-E6 and the charger is the LC-E6.There is also the LP-E6NH, and with the advent of the R5markii a new battery, the LP-E6P has been introduced.
The original LP-E6 is marked 7.2 volts and 1800 mAh. the newer batteries are rated 2100 mAh and may be marked 8.4 volts.
The 2.1.0 firmware for the R5 supports the new LP-E6P. It is possible to use the LP-E6P without upgrading the firmware, but continuous shooting speeds may be reduced.
Note that 7.2 volts is 2*3.6 and 8.4 volts is 2*4.2. The battery contains two Li-ion cells in series.
It has always been confusing how comapanies mark batteries using Li-ion cells. A battery marked 3.6 actually is 4.0 volts fully charged. I have seen makers mark such cells as 3.6 or 3.7 volts and it is all the same.
Some cells with greater capacity can be charged to 4.2 volts (at full charge). Canon adds to the confusion by marking one battery for the "average" voltage over the discharge cycle, and the other for the 8.4 max charge. To be consistent they should mark one 8.0 and the other 8.4.
This begs the question of what the LC-E6 charger does. I have not made measurements, but my prediction is that it will charge either battery to 8.0 volts total and sacrifice some of the capacity of the new battery. I might be surprised, but I will be surprised if I am surprised.
Tom's Digital Photography Info / tom@mmto.org