Battery Info

Batteries are an area of confusion, but there is very little to be confused about if we break them down.

Voltage

Batteries are made up of cells (imagine these as AA alkaline batteries in your TV remote), each cell holds 3.7 volts. The number of cells in a battery is shown by the letter S. A typically battery will be a 3 or 4 cell. i.e. 3S or 4S. So a 3S has 11.1 volts and a 4S has 14.8 volts (so far so good eh?)

  • 3.7 volt battery = 1 cell x 3.7 volts (1S)
  • 7.4 volt battery = 2 cells x 3.7 volts (2S)
  • 11.1 volt battery = 3 cells x 3.7 volts (3S)
  • 14.8 volt battery = 4 cells x 3.7 volts (4S)
  • 18.5 volt battery = 5 cells x 3.7 volts (5S)
  • 22.2 volt battery = 6 cells x 3.7 volts (6S)
  • 29.6 volt battery = 8 cells x 3.7 volts (8S)
  • 37.0 volt battery = 10 cells x 3.7 volts (10S)
  • 44.4 volt battery = 12 cells x 3.7 volts (12S)

NEVER let your batteries fall below 3.5v per cell (so for a 3S 10.5 volts), if a battery falls below this it will be damaged. This is where your storage charge comes in. When you are not using your batteries for a few days make sure you storage charge them. The reason being that batteries naturally discharge over time. If you leave your batteries in a discharged state over time they will drop below the 3.5volt mark and the damage will be done.

Equally never leave them fully charged, the chemical reaction that takes place in the batteries will cause damage and significantly reduce your battery lifespan.

The best option is to store batteries at room temperature at a 50% charge.

A fully charged cell holds 4.2volts,  therefore for a 3S (3.7 volts per cell x 3 = 11.1 volts). The 100% charge voltage of this LiPo pack = 12.6 volts (4.2 volts x 3 = 12.6 volts).

Capacity

The next number (mAh) is the reference to the capacity of the battery (basically how long they can last for). A battery’s capacity is rated in mAh or milliamp hours (1000th of so a 2200mAh battery will provide 2.2amps over the period of 1 hour – 2200/1000 = 2.2) . A 2200 mAh battery is rated to deliver 2200 mAh (or 2.2 amps) per  hour i.e. if a load of 2200mAh was placed on the battery, it would be fully discharged within an hour.

Generally a bigger mAh value will increase your flight duration, however the bigger the mAh the heavier the battery (when you gain something you typically lose something else).

Discharge Rate

The other rating on a batter is the C rating. C rating is the discharge rate. This is the number of time the batteries average that you can safely use in one ‘cycle’.

A battery with a discharge rating of 20C would mean you could theoretically & safely discharge it at a rate 20 times more than the capacity of the pack, a 20C pack = 20 times more, a 35C pack = 35 times more, and so on.

If a battery has a rating of 2200 mAh and a discharge rating of 20C, then you could pull a maximum sustained load up to 44,000 milliamps or 40 amps off that battery (20 x 2200 milliamps = 44,000 milliamps or 44 amps).

While there is little point in buying a battery with a very large discharge rate (unless of course you are pulling high amps) it is very important you do not buy a battery with a too low discharge rate. If you try and pull too many amps you will kill the battery (and possibly your electronics).

Remember, Voltage gives you “thrust”, Amps allows you to life heavier aircraft.

For example, if you have this battery: Turnigy 4000mAh 3S 30C Lipo Pack

It can handle 4000mAh * 30C draw. That is 4000*30 = 120000 mAh draw. That means it can take 120 Amps being drawn form it. With a quadcopter (4 motors) the max draw the battery can take is 30 Amps (120 / 4 = 30).

Drawing more than that can cause damage to the battery. Drawing too much less than this is also not good for the battery. That is why they sell low C batteries for transmitters.

battery-connectors

The main picture above (replicated with permission from http://radioactivemodels.ie shows a range of the most popular battery connectors and balance / charging plugs. They are labelled and listed as follows :

  • B1  – Deans (T) type main connector – Female & Male. Used for main connection to speed controllers and motors. Used for medium to high current draw
  • B2  – JST / BEC type main connector – Female & Male. Used for main connection to speed controllers and motors. Used for low current draw
  • B3  – Tamiya main battery plug usually used on Car and Boat batteries (NiCd / NiMh) – Female & Male
  • B4  – Bullet Connectors – Female & Male. Single wire connectors, available in a range of different sizes to suit current draw / load requirements from 2mm to 8mm
  • B5  – HXT Connectors – Female & Male. Available in 3.5mm and 4.00mm sizes. Used for main battery connectors for medium / high power applications
  • B6  – Traxxas Connectors – Male & Female. Mainly used on high current draw car and boat batteries
  • B7  – XT60 Connectors – Male & Female. Used for high current draw battery connections
  • B8  – EC3 Connectors – Male & Female. Used for high current draw battery connections
  • B9  – Flight Power / Thunder Power (FP / TP) LiPo Balance Charger plug – Female & Male
  • B10 – Hyperion / PolyQuest (HP / PQ) LiPo Balance Charger plug – Female & Male
  • B11 – JST-XHR (XH) LiPo Balance Charger plug – Female & Male
  • B12 – JST-EHR (EH) LiPo Balance Charger plug – Female & Male