Method of Estimating Surface Ion Density

A battery charging device for a battery comprising:

• a battery;
• a battery charger for charging the battery;
• and
• a charging control means comprising a machine implemented method for estimating the ion density of the surface of either positive or negative electrode of the battery, the machine-implemented method comprising:
• dividing each electrode into N layers of active electrode material;
• determining a battery current applied to the electrode of the battery;
• determining the ion density variable for each one of the N layers of the active electrode material;
• and
• determining the ion density of the electrode surface, and
• wherein the ion density variable of each of the N layers of the active electrode material comprises a function of the difference between the respective ion density variables of adjacent N layers, and
• wherein the ion density of the electrode surface comprises a function of the battery current and the difference between the respective ion density variables of adjacent N layers.