Patent ID: 7990276

Claim:
A battery charger comprising: a first electrical contact that receives a positive contact of an attached battery pack; a second electrical contact that receives a negative contact of the attached battery pack; a plurality of inter-cell electrical contacts that selectively receive inter-cell contacts of the attached battery pack, wherein the inter-cell contacts of the attached battery pack are connected to nodes between cells of the attached battery pack; a measurement module comprising: a multiplexer that connects a selected one of the first and second electrical contacts and the plurality of inter-cell electrical contacts to an output terminal; an analog to digital converter that receives contact voltages from the output terminal of the multiplexer and digitizes the contact voltages; and a voltage determination module that determines a cell voltage of each of the cells of the attached battery pack based on the digitized contact voltages; and a control module that: estimates a first number of total cells contained in the attached battery pack by subtracting a second number from a maximum number of cells, wherein the second number represents how many of the inter-cell electrical contacts the measurement module detects are disconnected; prevents charging the attached battery pack when the measurement module detects that one of the plurality of inter-cell electrical contacts is disconnected and a product of the first number and the first voltage differs from an overall voltage of the attached battery pack by more than one of a predetermined voltage and a predetermined percentage; stores a plurality of acceptable profiles of disconnected inter-cell electrical contacts and prevents charging the attached battery pack when the digitized contact voltages of the inter-cell electrical contacts do not match one of the plurality of acceptable profiles; and prevents charging the attached battery pack when any two of the cell voltages differ from each other by more than one of a predetermined voltage and a predetermined percentage; and a light source that blinks in one of a set of predefined patterns when charging is prevented.