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What Are Lithium Polymer (LiPo) Batteries, and Are They Better Than Nimh Batteries?
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What Are Lithium Polymer (LiPo) Batteries, and Are They Better Than Nimh Batteries? - 02.05.2006, 02:56 PM

Lithium Polymer (LiPo) is a different chemical composition than standard Nickel-Metal Hydride (Nimh) sub-c batteries typically used in radio control vehicles.

LiPo has a higher energy density than Nimh and can therefore provide more power in less overall space. An example would be comparable battery packs: a 6-cell Nimh battery pack (3300mah) will provide 7.2V nominal at a size of approximately 140mm L, 51mm W, 19mm H, and a weight of approximately 400g.
A 2-cell LiPo battery pack (3200mah) will provide 7.4v nominal at a size of approximately 130mm L, 42mm W, 16mm H, and a weight of approximately 200g.

LiPo battery cells are packages in a thick, foil-like wrapping and typically held together with thick heat-shrink or a plastic case.

LiPo batteries are sensitive to over-charging and over-discharging. If over-charged, a LiPo battery may swell and catch fire. If over-discharged, the LiPo battery may become damaged and become incapable of being charged to full capacity again.

LiPo batteries MUST be charged on a LiPo-compatible charger at the manufacturer's recommended charge rate (typically 1C). A 1C charge means to charge the battery at 1x it's capacity. For example, a 3200mah battery would need a 3.2 Amp charge to charge at 1C; 3200 milli-amps = 3.2 amps. Cutoff for charging should be set at 4.2 volts per cell (if the charger does not have an automatic setting).

LiPo batteries have a much lower self-discharge rate than Nimh batteries have. This means that a fully-charged LiPo battery will keep it's full charge for hours, days, maybe even weeks, without having to be re-charged. Comparitively, a Nimh battery can lose up to 25% of it's full charge after being stored for just one week without usage.

LiPo batteries should never be discharged below 2.7 volts per cell. Over-discharging may damage the batteries and permanently decrease their capacity and performance. Several speed controllers have a voltage cut-off setting for LiPo batteries, and several manufacturers sell LiPo Low-Voltage Cut-Off devices.

Please note that this information is intended to provide you with basic information in regards to Lithium Polymer batteries and is NOT a replacement for manufacturers instructions and guidelines for usage of their LiPo batteries/chargers.

PLEASE FOLLOW THE MANUFACTURERS INSTRUCTIONS FOR CARE AND MAINTENANCE OF LITHIUM POLYMER BATTERIES.

More replies to will follow in this thread to provide more LiPo-specific information.


Joe

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