Everything you need to know about RC Batteries

Everything you need to know about RC Batteries

NiMH & LiPo
There are two essential types of batteries used to power electric models: Nickel-Metal Hydride (NiMH) and Lithium Polymer (LiPo). The chemistry-class names refer to the essential materials within the battery that react to store and release energy as electricity, and each has its pros and cons.

NiMH
If you purchased a ready-to-run (RTR) model with an included battery, chances are it’s a NiMH. Nickel-metal packs are rugged, inexpensive, and don’t require much in the way of special care. However, they’re heavier than a LiPo battery of similar voltage and capacity (we’ll get to those terms), and their voltage decreases steadily as the pack is discharged. Once you start driving, your car goes slower with each passing minute. Not noticeably at first, but steadily.

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NiMH packs are constructed with cylindrical cells (usually 6-8 of them) like those we’ve been dropping into flashlights and TV remotes for years.

 

LiPo
LiPo batteries are generally sold as accessories, but there are RTR models that include them. A LiPo battery is lighter than a NiMH of similar voltage and capacity, which helps your model feel more powerful. Also contributing to that “feeling of power” (often called “punch”) is the LiPo’s ability to maintain its voltage longer as the pack is depleted. Instead of delivering less and less voltage throughout your run, a LiPo will hold a steady voltage for most of your run, then fall off quickly at the end of the charge. The downside is cost (LiPos are more expensive than NiMH, but the gap is narrowing), and care — LiPos require a specific care regimen for longest life and safe use.

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LiPo batteries are assembled with flat slab-like cells. Most LiPos used in RC cars are 2- or 3-cell configurations.

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CAPACITY & VOLTAGE
The important things to consider when looking at batteries, whether NiMH
or LiPo, is their capacity (which determines how long your car or truck
will run per charge) and voltage (which determines how much speed and
power your model will deliver). Here’s what you need to know:

Capacity
The big number on the battery label (3300, 4000, 5000 etc.) indicates its capacity in milliamp hours, which is generally shortened to “mAh.” The greater the number of mAh, the longer your car will run per charge (and conversely, the longer it will take to recharge the pack). “Bigger number = longer run time” is all you really need to know, but it’s helpful to understand what the mAh rating actually means. If your battery is rated at 5000mAh, that means it can hold a steady 5-amp load for a full hour. We get “5” from “5000” because a milliamp is 1/1000 of an amp. Divide the mAh rating by 1000, and you get amps. 5000 ÷ 1000 = 5. If you have a 6000mAh battery, it can hold a 6 amp load for an hour. Or, if you put it on a 5 amp load, it will run longer than an hour. See? Greater capacity = longer run time.

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You’ll find two important numbers on any battery: capacity (here, 5250mAh) and voltage (7.4V for this MaxAmps pack).

 

Voltage
As with capacity, more volts is better—to a point. Your vehicle’s power system is designed to handle a certain amount of voltage, and exceeding that voltage will (at the very least) shut the system down if it has “over voltage protection,” or (at worst) fry the electronics. So, check your speed control’s specs!
The voltage of a battery pack is determined by how many cells it has. A single NiMH cell delivers 1.2 volts, and NiMH batteries are most commonly offered with six or seven cells. These may be referred to as “6-cell” and “7-cell” packs, or they may be referred to by their voltage: 7.2 volts and 8.4 volts (since 6 x 1.2 = 7.2, and 7 x 1.2 = 8.4).

It’s different with LiPos. The principle is the same, but since a single LiPo cell delivers 3.7 volts, LiPo packs have fewer cells for a given voltage. The most common configurations are 2-cell, 7.4-volt packs (2 x 3.7 = 7.4) and 3-cell, 11.1V packs. Depending on your model and how much voltage it can handle, you may even be able to use 4, 5, or 6-cell packs—again, check those power-system specs!

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What About “S”?
As we just discussed, NiMH and LiPo packs are often referred to by the number of cells in the pack: for example, “2 cell” or “3 cell.” You may also see or read about LiPo packs with a designation such as 2S, 3S, 4S, etc. In this case, the “S” refers to series, and indicates that the cells within the pack are connected “positive to negative,” like in the illustration below. Some LiPo packs features cells connected both in series and in parallel, which is designated by a “P.” For example, a “2S2P” LiPo pack would have two pairs of LiPo cells inside. Each pair would be wired in parallel (2P), and the two pairs would be wired together in series (2S). Is your head hurting? Don’t worry about it. Nearly every RC LiPo is wired in series and simply referred to as 2S, 3S, 4S, etc.

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With its covering removed, we can see the two stacked cells of this “2S” LiPo. The cells have been tinted so you can easily distinguish them.

 

RC Car Action - RC Cars & Trucks | Everything You Need to Know About RC Batteries
When cells are connected in series, their voltages are combined. This illustration shows a “2S” pack: two 3.7 volt cells in series. The cells are connected by their positive (+) and negative (-) tabs to deliver 7.4 volts at the connector.

 

(Source: https://www.rccaraction.com/everything-need-know-rc-batteries/)

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