Battery with a spare battery

Year	Description
1990	Invention patented by Masafumi Tanaka on December 23th, 1990. Abstract: A battery including a spare battery is provided in which the six cells conventionally used for the spare battery are decreased to three cells, thereby allowing the capacity of the main battery to be increased. No charger for the spare battery is required. The main battery comprises six cells connected in series, the first of the six cells having a capacity at least 10% higher than that the remaining three cells. A switch is used to connect the spare battery in parallel with the remaining three cells of the main battery.
Source: selected by the editor from original sources.

Invention: Battery with a spare battery