Patent ID: 7405537

Claim:
A method of estimating the remaining state-of-charge of a non-rechargeable power source configured as a back-up power source for an electronic module normally powered by a primary power source, comprising the steps of: a) calculating a self-discharge factor based on temperature; b) combining a nominal self-discharge rate of the non-rechargeable power source with the self-discharge factor and an initial state of charge of the non-rechargeable power source to produce a temperature-adjusted self-discharge quantity; c) calculating a quantity of parasitic leakage current draw from the non rechargeable power source; d) calculating a quantity of voltage sampling current draw from the non-rechargeable power source; e) calculating a quantity of transient current draw from the non-rechargeable power source; f) subtracting the temperature-adjusted self-discharge quantity, the quantity of parasitic leakage current draw, the quantity of voltage sampling current draw, and the quantity of transient current draw from the initial state-of-charge of the non-rechargeable power source to generate an estimate of a remaining state-of-charge of the non-rechargeable power source; and g) displaying the generated estimate to a user.