LiPo (Lithium Polymer) batteries have three main advantages over NiCad and NiMH batteries:
- Light weight
- Large capacities (holds lots of power in a small package)
- High discharge rates (powers demanding electric motors)
Downsides of using LiPo batteries:
- More expensive than NiCad or NiMH
- Don’t last for as many charges, especially if not cared for properly
- They can catch fire or explode easily if not cared for properly
Voltage
LiPo batteries are rated at 3.7 volts per cell.
- 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)
(?S) = how my cells hooked in series (S) the battery pack contains
“3S2P” would indicate 2, three celled series packs hooked up in parallel to double the capacity.
Capacity
Capacity indicates how much power the battery pack can hold and is indicated in milliamp hours (mAh). A LiPo battery that is rated at 1000 mAh would be completely discharged in one hour with a 1000 milliamp load placed on it. Basically, if you want more flight time; increase the capacity of your battery pack; but be careful because as you increase, the weight of the pack also increases, which isn’t good for flight.
Discharge Rate
Go with 20C to 25C rated battery packs for general to light sport flying. For larger planes, go with 25C to 30C and for agressive sport flyers, use 35C to 45C discharge ratings on your batteries.
The general rule is if you can’t comfortably hold a LiPo pack tightly in your hand after using it, it’s too hot.
The Number One Killer of LiPo’s: Over Discharging
This simply means that you should never discharge a LiPo pack down past 80% of it’s capacity to be safe. If you have a 2000 mAh LiPo pack, you should never draw more than 1600 mAh out of the pack (80% x 2000). This is assuming a healthy pack as well that has the full 2000 mAh capacity (as packs age, their capacity drops).
Charging LiPo Batteries
A 3.7 volt RC LiPo battery cell is 100% charged when it reaches 4.2 volts. It is critical that you use a charger specified for Li-Po batteries and select the correct voltage or cell count when charging your RC LiPo batteries. Never charge a LiPo or Li-Ion pack greater than 1 times its capacity (1C).
The three main things that shorten LiPo battery life are: Heat, Over-Discharging, and Inadequate Balancing.
Get a battery charger that can do balancing and do the balancing on the battery every other time you charge it.
For optimum battery life, store your RC LiPo batteries at room temperature and at about 40-60% charged. That equates to around 3.85 volts per cell (open terminal resting voltage).
LiPo Battery, Charger & Balancer ($252):
- Battery ($69): FlightPower EONX Lite LiPo 3S 11.1V 2500mAh 25C
- Charger ($170): Triton2 EQ AC/DC
- Charger > Battery ($6.25): Charge Lead Banana Plugs/Deans Male Ultra
- Balancing Board ($6): Triton EQ Bal Board FlightPower