The nickel-metal hydride battery voltage is 1.2V, and the lithium battery voltage is 4.2V. The latter is larger than the former, and the former is larger than the latter.
Rechargeable lithium battery is widely used in many new mobile devices because it has the advantages of small size (relative), light weight, low self-discharge rate and no memory effect compared with ordinary nickel-cadmium/nickel-hydrogen batteries.
The lithium battery has a large specific energy and a small battery; the voltage of a single lithium battery is three times that of a nickel-hydrogen battery; there is no memory effect, and it can be used as needed. But you can't use it to charge it, so the number of times of charging and discharging is too much, which affects the battery life.