Abstract: A battery charging system 100 is provided which comprises a charger 101 and a battery pack 102. The battery pack 102 comprises a battery cell or cells 150, memory means 140, temperature sensing means 147, and a high accuracy, high impedance voltage sensing means 112 that senses voltage directly at the battery cell terminals 151, 149. By sensing directly at the cell terminals 151, 149, charging error due to parasitic conductor impedances 132, 138 can be eliminated. The voltage sensing means 112 allows memory 140 and thermistor 147 data to be multiplexed, allowing the system to operate with four or fewer battery terminals.

Abstract: An adapter system comprising an adapter with plug prongs on its front face and apertures on its back face, and adapter contacts within it, and a power supply with power supply prongs disposed outwardly, which prongs have undercuts at their distal ends; where the power supply contacts can be inserted into the apertures of the adapter, and the adapter is then rotated around the axis of insertion, mechanically securing the adapter to the power supply and simultaneously making electrical contact between the adapter and the power supply.