Capacity rating Cell capacities are rated in ampere hours (A·h) or milliampere hours (mA·h). A 1000 mA·h battery is the same as a 1 A·h battery: both will supply 1 A for 1 hour. The C rating commonly associated with lithium ion batteries refers to the maximum current supply capability as a multiple of the cell's capacity: for instance, a 1 A·h, 20C battery should be able to supply 20 A continuously without damage. A useful way to calculate how long a battery will last for under heavy load is to multiply the A·h capacity by 60 to give ampere-minutes, so a 1 A·h battery is a 60 ampere-minute battery; to calculate how many minutes the battery will last, just divide by the average current drawn (e.g. a 10 A average current draw will mean that a 60 ampere-minute battery will last for 60/10 = 6 minutes).
An ampere hour is equal to 3600 coulombs, the standard SI unit for amount of electrical charge. The amount of energy stored depends on the voltage, and is equal to the voltage times the charge in coulombs, or 3600 times the voltage times the charge in ampere-hours. So, a 10 A·h battery pack with a nominal voltage of 10 volts would deliver 36,000 coulombs of charge (or 2.2×1023 electrons), and 360 kJ of energy (360 kJ = 100 W·h).
Charging LiPoly batteries must be charged carefully. The basic process is to charge at constant current until each cell reaches 4.2 V; the charger must then gradually reduce the charge current while holding the cell voltage at 4.2 V until the charge current has dropped to a small percentage of the initial charge rate, at which point the battery is considered 100% charged. Some manufacturers specify 2%, others 3%, but other values are also possible. The difference in achieved capacity is minute.
Balance charging simply means that the charger monitors the voltage of each cell in a pack and varies the charge on a per-cell basis so that all cells are brought to the same voltage.
It is important to note that trickle charging is not acceptable for lithium batteries; Li-ion chemistry cannot accept an overcharge without causing damage to the cell, possibly plating out lithium metal and becoming hazardous. Most manufacturers claim a maximum and minimum voltage of 4.23 and 3.0 volts per cell. Taking any cell outside these limits can reduce the cell's capacity and ability to deliver full rated current.
Most dedicated lithium polymer chargers use a charge timer for safety; this cuts the charge after a predefined time (typically 90 minutes).
Storage Unlike certain other types of batteries, lithium polymer batteries can be stored for one or two months without significantly losing charge. However, if storing for long periods, manufacturers recommend discharging the battery to 40% of full charge. In addition, other sources recommend refrigerating (but not freezing) the cell
Lithium Polymer Batteries
