A method, comprising: receiving a user's selection of a charging criterion for balancing stored charges in a first device's own battery and in a second device's rechargeable battery; determining that recharging of the second device's rechargeable battery is required; computing an amount of charging required for the second device's rechargeable battery in order to satisfy the user's selected charging criterion; and transmitting, by the first device, power provided by the first device's own battery, to the second device, for charging the second device's rechargeable battery until the present level of stored battery charge in the second device's rechargeable battery reaches the computed amount of charging required, characterized in that: the receiving the user's charging criterion, the determining that recharging is required and the computing the amount of charging required are performed by the first device; and in that the method further comprises accessing, by the first device, a database, to retrieve battery characteristic data for at least one of the first device's battery and the second device's battery, including at least one profile of different power consumption with different use cases; and computing the amount of charging required for the second device's rechargeable battery is done based on the at least one profile of different power consumption with different use cases. receiving a user's selection of a charging criterion for balancing stored charges in a first device's own battery and in a second device's rechargeable battery; determining that recharging of the second device's rechargeable battery is required; computing an amount of charging required for the second device's rechargeable battery in order to satisfy the user's selected charging criterion; and transmitting, by the first device, power provided by the first device's own battery, to the second device, for charging the second device's rechargeable battery until the present level of stored battery charge in the second device's rechargeable battery reaches the computed amount of charging required, characterized in that: the receiving the user's charging criterion, the determining that recharging is required and the computing the amount of charging required are performed by the first device; and in that the method further comprises accessing, by the first device, a database, to retrieve battery characteristic data for at least one of the first device's battery and the second device's battery, including at least one profile of different power consumption with different use cases; and computing the amount of charging required for the second device's rechargeable battery is done based on the at least one profile of different power consumption with different use cases. the receiving the user's charging criterion, the determining that recharging is required and the computing the amount of charging required are performed by the first device; and in that the method further comprises accessing, by the first device, a database, to retrieve battery characteristic data for at least one of the first device's battery and the second device's battery, including at least one profile of different power consumption with different use cases; and accessing, by the first device, a database, to retrieve battery characteristic data for at least one of the first device's battery and the second device's battery, including at least one profile of different power consumption with different use cases; and computing the amount of charging required for the second device's rechargeable battery is done based on the at least one profile of different power consumption with different use cases.