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Wiki: LiPo batteries

What are LiPo batteries?

LiPo batteries (lithium polymer accumulator) are rechargeable batteries that play an important role in model making and in the field of embedded and DIY electronics. Wearables and e-textile projects for Arduino and Raspberry Pi often work with LiPos in order to be independent of a fixed power supply. Almost everyone of us comes into contact with one of the most famous areas of application for LiPo batteries - the mobile phone!


Advantages of LiPos compared to conventional batteries

LiPo batteries have five main properties that make them the ideal battery for DIY projects:

  • LiPo batteries are lightweight and can be made in almost any shape and size.
  • LiPo batteries have large capacities, i.e. they store a lot of energy in a small package (high energy density).
  • LiPos are very good at maintaining a consistent voltage / power output when discharging. However, the voltage / power drop when they reach a fully discharged state is very rapid compared to NiCd, NiMh or PB.
  • LiPo batteries have high discharge rates to power the most demanding electrical projects. LiPos also enable high charging current rates, so that charging is possible in a short time.
  • In contrast to NiCad or NiMh, LiPos have no "memory effect".


What do voltage and cell count mean?

A single LiPo cell is rated at 3.7V. You will see almost 4.3V on the cell when fully charged, but it quickly drops to 3.7V with normal use. When it is depleted the cell will be around 3V. That means your project will have to handle different voltages when working directly from a cell. If you need 5V, you have to combine two LiPos in series to get a 7.4V pack and regulate it to 5V.

(Source: ProTalk.net)


The voltage of a battery, for example, determines how fast a vehicle drives. The voltage directly influences the speed of the electric motor (brushless motors are rated at kV, which means "speed per volt"). So if you have a brushless motor that is 3,500kV, that motor spins 3,500rpm for every volt you apply, and with a 2S LiPo battery, this motor spins 25,900rpm.

Here is a list of commonly used lipos with cell numbers:

  • 3.7 volt battery = 1 cell x 3.7 volt (1S)
  • 7.4 volt battery = 2 cells x 3.7 volt (2S)
  • 11.1 volt battery = 3 cells x 3.7 volt (3S)
  • 14.8 volt battery = 4 cells x 3.7 volt (4S)
  • 18.5 volt battery = 5 cells x 3.7 volt (5S)
  • 22.2 volt battery = 6 cells x 3.7 volt (6S)


With the number in brackets means, the battery manufacturers indicate how many cells in row ā€œSā€ contains the battery pack.

Batteries can also wired in parallel to increase the capacity. This is indicated by a number followed by a "P". Example: 3S2P would display 2 x 3-cell series packets connected in parallel to double the capacity.


What does capacity mean?

The capacity indicates how much current the battery can hold and is specified in milliampere hours (mAh). This is how much load or loss (measured in milliamps) is possible for 1 hour.

For example, a lipo battery rated at 1000 mAh would be completely discharged in one hour when a load of 1000 milliamps is applied. If a 500 milliamp load was applied to the same battery, it would take 2 hours to empty. If the load were increased to about 15,000 milliamps (15 amps), the time to discharge the battery would only be about 4 minutes.


What does the C rate mean?

Almost all of the lithium polymer batteries you buy today are rated ā€œCā€. The C in C rate stands for capacity. The C-rate is the maximum, safe, continuous release rate of a package according to the manufacturer's instructions. So if you see 20C printed on your label, it means it can be "continuously" discharged at 20 times the pack capacity. Capacity is usually measured in mAh and a popular cell size is 2200 mAh, for example:

  • 2200mAh 20C cell = 2.2A x 20 = 44A continuous discharge

Along with the continuous rate of discharge, some batteries will display a 'burst' rate of discharge. This is typically twice the continuous rate of discharge. This usually means that the battery will allow double the amperage, but only for a few seconds.



Connections (connectors)

Most LiPos use 2-pin connections, but they can be very different in design. All of our LiPo batteries use a 2-pin JST-PH connector with a 2.00 mm pitch (data sheet). This connection is compatible with our lipo chargers and development boards.


Safe charging and discharging of LiPo batteries: Lipo-Charger

It is important to use a LiPo compatible charger for LiPo batteries, as LiPo batteries require special care and can explode if handled improperly. Basically, the charger keeps the charging current constant until the battery reaches its peak voltage. Then this voltage is maintained while the current is reduced.

There are many inexpensive chargers for charging LiPo batteries. These often use USB to charge the battery. Do not try to charge LiPos without a charger. A LiPo battery can be damaged by overcharging. You should therefore use a specially developed LiPo charger, a so-called LiPo charger. In our category of the same name you will find a large selection of such "lipo chargers".

LiPo batteries can also be damaged if they are discharged too far. To protect against this, almost all LiPo batteries have a small safety circuit at the top of the cell that switches off the battery when the voltage drops below a certain threshold (usually 3V).

LiPo batteries have a very low internal discharge rate. This makes them a good candidate for projects that have low power requirements and need to run for many days or months.


>>> Buy the right 3.7 V LiPo batteries for your next project!