The output voltage is different. The voltage of the nickel-metal hydride battery is much lower than the voltage of the lithium battery of the same specification, so the output of the same power, the current output of the nickel-hydrogen battery is much higher, P=U*I, power=voltage X current.
The output of a battery's current determines the length of use of this battery. For example, a battery of 800mAH means that the battery can be continuously released for one hour at a current of 800mA. Under the same output power, for example, to drive the same power fan, the nickel-hydrogen battery has to be released because of the low voltage. Large currents to drive, such as the need for 100mA to drive, then only 8 hours, and lithium batteries because of the high voltage, only 10mA current can reach the power of a fan, so the lithium battery can be used for 80 hours.