Determining battery depletion for coordinating battery replacement

A method comprising:

• conducting, by a battery controller of a battery-powered node in a mesh network, electrical energy from a primary cell to a secondary cell at a current level that is independent of a load resistance of the secondary cell;
• and
• transmitting, by the battery controller to a server, an amount of time during which the electrical energy is conducted from the primary cell to the secondary cell, wherein the amount of time is usable by the server to determine an amount of battery power stored in the primary cell.

One or more non-transitory computer-readable media storing instructions that, when executed by one or more processors, cause the one or more processors to perform the steps of:

• recording an amount of time during which electrical energy is conducted from a primary cell to a secondary cell at a current level that is independent of a load resistance of the secondary cell, wherein the amount of time is usable to determine an amount of energy stored in the primary cell.