In this article we discuss the main features of a LiPo battery: Voltage, Capacity, C of discharge and charge, number of Series and Parallel elements, and Watt-hour.
Let's look in detail at what these data stand for.
Voltage
The battery voltage is given in volts (V) and depends on the number of elements in series in the pack. It is always a multiple of 3.7 V (3.8 in HV batteries).
Capacity
The capacity of a battery can be considered the size of the "tank" and thus gives an indication of the duration of discharge.
Capacity is the current times the discharge time at that current rating, so, for example, a 5000 mAh battery can provide a current of 5 amps for 1 hour, 10 A for 1/2 hour, 2.5 A for 2 hours, etc.
Discharging C rating
Discharging C rating indicates the multiple of the capacity to achieve the maximum current that the battery can safely maintain continuously. For example, a 50 C battery of 4000 mAh (4A), can deliver the maximum current of 200A (Imax = 50 x 4A = 200A).
Sometimes manufacturers indicate two values of C; the higher indicates the peak current (burst) that the battery can withstand for short periods.
Discharge C rating is an indicator of battery quality; the higher it is, the higher the battery's performance at high draws. However, it is also a safety indicator because it provides information about the current that should not be exceeded.
Charging C rating
Charging C rating indicates the multiple of the capacity to achieve the maximun charging current recommended by the battery manufacturer. When it is not specified, we recommend not to exceed charging at 1C, which requires a charging time of about 1 hour. Using a 3000 mAh battery as an example, charging at 3000 mA (3A) will complete the charge in about 1 hour.
Some manufacturers allow charging at currents higher than rated. In any case, the limits specified by the manufacturer should never be exceeded, and it is always a good idea to use fireproof bags.
S (series) and P (parallel) cells connections
The single element in a battery is called cell and its voltage is always 3.7 V (3.8 le HV).
Cells can be used individually or assembled in identical cell packs to provide multiple voltages and capacities over the single cell.
S and P indicate the assembly configuration of the battery pack. In an nSmP pack there are n sub-packs connected in series, each consisting of m cells connected in parallel; the total number of cells is therefore n x m.
S and P configuration is a building data and usually influences neither the choice of battery nor the handling during use.
Watt-hour
This data indicates the electrical energy stored in the battery and matches the electrical power (in watts) that the battery can supply constantly, over the time of 1h. If the required power doubles, the duration is halved and vice versa.
Since power is voltage times current, energy is voltage times capacity: 1Wh = 1V x 1Ah.
Although this data is redundant and derived from the others, some manufacturers prefer to report the Wh on the label without needing to calculate it.
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