above 4.30V, the cell causes lithium metal plating on the anode; the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Overcharging causes the cell to heat up. Much attention has been placed on the safety of Li-ion to prevent over-charge and over-discharge. Commercial Li-ion battery packs contain a protection circuit that prevents the cell voltage from going too high while charging. The upper voltage threshold is typically set to 4.30V/cell. Temperature sensing disconnects the charge if the cell temperature approaches 90C (194F); and a mechanical pressure switch on many cells permanently interrupt the current path if a safe pressure threshold is exceeded. Exceptions are made on some spinel (manganese) packs containing one or two small cells. The charge process of a Li-ion Polymer is similar to Li-ion. These batteries use a gelled electrolyte to improve conductivity. Charging at High and Low Temperatures Rechargeable batteries work under a reasonably wide temperature range. This, however, does not automatically permit charging at these extreme conditions. While hot or cold temperatures cannot always be avoided, recharging a battery is at the control of the user. Efforts should be made to charge at room temperatures. No commercial battery should be charged below freezing. Nickel-based batteries should only be fast-charged between 10C to 30C (50F to 86F). Below 5C (41F), the ability to recombine oxygen and hydrogen is greatly reduced and the resulting pressure build up may cause the cells to vent. The charge acceptance of nickel-based batteries at higher temperatures is drastically