Lithium Polymer battery
A battery chemistry known as Lithium Polymer. The electrolyte in a LiPo battery is a polymerized form of lithium. LiPo cells have a nominal voltage of 3.7v per cell. LiPo batteries offer very high power output per gram of weight, but are somewhat costly and very intolerant of mistreatment. Overcharging or over-discharging a LiPo battery will destroy it, sometimes spectacularly. LiPos have become the cell chemistry of choice for the flying RC hobbies.
A Lipo cell has a maximum voltage of around 4.20V; much above this and it will quickly heat up and may 'vent with flame'; a prolonged short-circuit may also cause this. The voltage to avoid discharging below is usually considered to be 3.0V while under load; however the usual advice is to avoid discharging a cell by more than 80% of its capacity, which will typically take the cell down to around 3.7V
A Lipo battery consists of a number of cells in series and/ or parallel connection. The notation 3S1P describes a battery of 3 cells connected in series; similarly 3S2P would describe a battery of 6 cells, consisting of 3 sets of two parallel cells (1S2P batteries) connected in series.
As lipos are so intolerant to overdischarging and overcharging, it is important to ensure that each cell is charged properly. The best way to do this is with a balance charger which connects to the battery's balance connector. The battery connects to the ESC, BEC and other electronics via one of a number of different discharge connectors.
A battery will have a discharge rating specified by the manufacturer. Usually both a continuous discharge, and peak (temporary) discharge rating are given, sometimes in Amperes, sometimes as a C rating. Exceeding this can damage the battery, in the worst case explosively.
Like all batteries, LiPo's 'wear' with repeated use, losing capacity. Charging at rates exceeding 1C and fast discharging (even within the LiPo's rated capacity) will accelerate the wear. For reasonable lifespans, balance charge at no more than 1C, and discharge at an average of no more than half the pack's rated continuous discharge rate, to a voltage of 3.8V per cell when not under load.
When not using Lipo batteries for a long time, the ideal way to store a battery is to store it at 0'C (32F) at a 40% charged state. The temperature can also be room temperature as this is not too critical, but the 40% charged state is more important. You may store the battery in a refrigerator (not the freezer). Storing a battery at a 100% charged state or storing it at high temperatures will decrease battery life. For more information, click here.
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