A method for determining a wear value of a battery of a mobile electronic device, the method comprising: using historical battery status data to estimate an actual capacity Q act of the battery; and using a design capacity Q des of the battery and the estimated actual capacity Q act of the battery to determine the wear value of the battery, wherein the historical battery status data comprises time information and battery charging status information, wherein the method comprises using the time information and the battery charging status information to identify one or more battery charge intervals (101, 102) during which the battery was charged, wherein the historical battery status data comprises a plurality of historical battery charge data points for each battery charge interval, and each historical battery charge data point comprises time information, battery charging current information, and battery charge information, wherein the time information comprises a relative time value or time stamp, wherein the battery charging current information comprises a value of charging current supplied to the battery, wherein the battery charge information comprises a fractional value of the actual capacity Q act of the battery, expressed as a fraction or as a percentage of the actual capacity Q act of the battery, characterised in that the method further comprises the following steps: identifying one or more battery charge ranges within each of the one or more battery charge intervals; determining, for each battery charge range, an estimate Q act ( k) of the actual charge capacity Q act of the battery, where k is an index assigned to each battery charge range according to the numerical order in which the fractional values of the actual capacity Q act of the battery in the battery charge ranges occur; and estimating the actual capacity Q act of the battery by averaging the estimates Q act ( k) of the actual capacity of the battery for all of the battery charge ranges according to the formula: Q act = 1 N k ∑ ∀ k Q act k where N k is the total number of battery charge ranges. using historical battery status data to estimate an actual capacity Q act of the battery; and using a design capacity Q des of the battery and the estimated actual capacity Q act of the battery to determine the wear value of the battery, wherein the historical battery status data comprises time information and battery charging status information, wherein the method comprises using the time information and the battery charging status information to identify one or more battery charge intervals (101, 102) during which the battery was charged, wherein the historical battery status data comprises a plurality of historical battery charge data points for each battery charge interval, and each historical battery charge data point comprises time information, battery charging current information, and battery charge information, wherein the time information comprises a relative time value or time stamp, wherein the battery charging current information comprises a value of charging current supplied to the battery, wherein the battery charge information comprises a fractional value of the actual capacity Q act of the battery, expressed as a fraction or as a percentage of the actual capacity Q act of the battery, identifying one or more battery charge ranges within each of the one or more battery charge intervals; determining, for each battery charge range, an estimate Q act ( k) of the actual charge capacity Q act of the battery, where k is an index assigned to each battery charge range according to the numerical order in which the fractional values of the actual capacity Q act of the battery in the battery charge ranges occur; and estimating the actual capacity Q act of the battery by averaging the estimates Q act ( k) of the actual capacity of the battery for all of the battery charge ranges according to the formula: Q act = 1 N k ∑ ∀ k Q act k where N k is the total number of battery charge ranges.