Lithium-Polymer batteries, otherwise known as “Lipo Batteries” are a newer type of battery used in many consumer electronics devices. If you’re looking for longer run times and higher power output, then Lipo Batteries are for you. These batteries offer a wide range of benefits. However, as in all things, one must weigh the pro’s and con’s to better understand the product and therefore determine if it’s the right needs based fit. In our humble opinion, you need longer run times and higher power output!
Let’s first talk about the differences between LiPo batteries and their Nickel-Cadmium and Nickel-Metal Hydride counterparts.
LiPo batteries offer three main advantages over the common Nickel-Metal Hydride (NiMH) or Nickel Cadmium (NiCd) batteries:
- LiPo batteries are weighing much less, and can be made in almost any size or shape.
- LiPo batteries have much higher capacities, allowing them to hold a lot more power.
- LiPo batteries have far greater discharge rates, meaning they pack a lot of punch.
On the flip side you have a few minor drawbacks.
• Shorter lifespan than NiMH/NiCd batteries. LiPos average about 300–400 cycles.
• Their sensitive-chemistry can lead to fire if the battery gets punctured.
• LiPo batteries need special care in the way they are charged, discharged, and stored.
Lipo Battery Numbers
All batteries have rating systems that tell you exactly the unique properties of the battery. These numbers are used to determine whether or not the battery is a right fit for given application. There are three Lipo Battery ratings that you need to be aware of.
Discharge Rating – “C” Rating
Voltage and capacity are easy to understand because they relate to speed or run time. Discharge, or “C” rating is a bit more complicated. The simplest understanding of C rating is – the rate at which the battery can be discharged safely. The part that complicates things is the number is derived from an equation that takes the capacity into account. With the Capacity rating in hand, use the following equation to determine maximum-safe continuous amp draw.
- 70C = 70 x Capacity (in Amps) Calculating the C-Rating of our example battery: 70 x 1.6 = 112A
So our equation results = 112A, which is the maximum sustained load that can safely be put on the battery. Any higher and you risk of degrading the battery at a faster pace, or even causing a meltdown.
Most batteries have two C ratings: continuous and burst. Burst ratings work the same except it relates to 10 second bursts only. So it tends to apply more to the acceleration period and not steady speeds. The burst rating is usually higher then continuous rating, and is not the usual reference for C ratings; commonly people are referring to the continuous rating.
Voltage and Cell Count
One Lipo cell has a normal voltage of 3.7V. So for our above battery there are 4 cells (4 x 3.7 = 14.8V.) The number of cells is referred to as “S Pack,” therefore, you would refer to this battery as a “4S Pack” battery.
The voltage of a battery pack is going to determine how fast your vehicle can go. Voltage influences the RPM of the motor (brushless motors are rated by kV, which means ‘RPM per Volt’). So with a brushless motor rating of 3,500kV, that motor spins at 3,500 RPM for every volt you applied. On a 2S LiPo battery, the motor spins 25,900 RPM. 3S batteries, spin at a whopping 38,850 RPM. So the more voltage, the faster you’re going to go.
The capacity rating has to do with the total power held by the battery. This number is represented by “mAh – milliamp per hour” rating. So like a car that only can drive as far as the gas it has in the tank, so too are batteries only able to go as far as their stored energy allows. It looks like this:
- 1000mAh = 1 Amp Hour (1Ah)
Naturally the higher the number the longer it can run before having to recharge. One factor you want to be aware of is to make sure to check engine temperatures if you use Lipo Batteries. Reason being the batteries long run time capability can easily lead to an engine overheating.
Finally, we get to a conclusion. These are the basics of Lipo Batteries. We could write a book on the subject, but the fundamentals will do for most RC enthusiasts. To us its real simple, if you want the highest performance possible, Lipo Batteries are the go to.