As full-size vehicles switch to battery power, this new power source brings with it new acronyms and units of measurement we need to wrap our heads around. But most remote control cars have always been battery powered. And as battery tech progresses, RC vehicles’ capabilities improve with it, as we discovered undertaking our RC rock crawler group test.
But what’s the difference between the battery types for RC cars? NiMH or LiPo batteries? That is why we’ve put together this guide: to answer such questions.
What is a battery?
A simple question, but so is ‘What does the word “a” mean?’ and most people would struggle with that, so we will begin right at the beginning.
A battery is a device that uses one or more cells and converts the electrochemical energy within those cells into electric energy. The scientific term for this process is an electrochemical oxidation-reduction reaction or redox reaction.
How does a battery work?
Electric energy is simply the flow of electrons, which creates a current. To get electrons flowing, they need to be going from one place to another (I was going to make the analogy about commuting to work and then realised a lot of us work from home now). These places electrons go to and from in a battery are the positive and negative electrodes, the anode and the cathode. And these electrodes consist of different metals. The force (voltage) and volume (current) of the movement of electrons determines the power of a battery.
When a battery is in use, the flow of negatively charged electrons needs to be balanced by a positive charge, and that is why batteries also have an electrolyte. The chemical products created by the reactions happening at both electrodes builds up and causes increased resistance to the overall reaction and eventually, the reaction stops, that is, the battery goes flat.
Some batteries use materials that allow the reaction to be reversed. Connecting lithium-ion, lithium polymer, or nickel-metal hydride batteries for example to an external power source sends energy back into the battery and the reaction can occur all over again. But rechargeable batteries cannot be recharged an infinite number of times. The electrodes degrade with each cycle and eventually don’t work anymore.
RC car battery types
Many combinations of materials have been used as electrodes in batteries, yet there is just a handful that has proven to be any good. Though, the ones used all have a range of different characteristics. The ones most commonly seen in RC cars are nickel-metal hydride (NiMH) and lithium polymer (LiPo) batteries.
NiMH batteries have a reasonable energy density that allows decent run times and compact size. They are robust and have a good life cycle, able to be recharged several hundred times before failing. However, NiMH batteries suffer from the ‘memory effect’, which means that they need to be fully discharged before recharging to maintain their capacity. Nickel-based batteries also have a relatively high discharge rate – around 10 to 15% per month.
LiPo batteries have even higher energy density and higher voltage, which means they give better run time, more power, and can be smaller. LiPo batteries also don’t suffer from the ‘memory effect’ and don’t have to be flat to be recharged. LiPo battery discharge rate is also less than NiMH batteries – around 5% per month. On the downside, they are more expensive than NiMH batteries and their lifespan is considerably less – they can be expected to last no more than 250 cycles.
If you’re wondering what the difference between LiPo and Li-ion batteries is, there are a few. LiPo batteries can be even more compact than Li-ion batteries and are more robust, hence their suitability for RC cars. But LiPo batteries are more expensive and don’t last as long. Fundamentally, LiPo batteries use a solid electrolyte, whereas Li-ion batteries use a liquid.
Using NiMH and LiPo batteries in RC cars
The main thing to remember is that LiPo batteries, although more immune to memory effect, cannot be fully discharged because they will be permanently damaged. This means that if you use a LiPo battery in your RC car, you need to enable the low-voltage cutoff on the vehicle’s electronic speed control (ESC). This feature will stop the LiPo battery is fully drained.
Your NiMH battery is more robust but if it’s new or has been sitting unused for a long time, it might suffer from false peaking. It’s just the way NiMH batteries are. A NiMH battery should be warm (not hot) to touch when fully charged. If it isn’t then you can repeat the charge cycle until it is. When using NiMH batteries, remember they need to be fully discharged to keep them in good condition.
What do the numbers on the battery packs mean?
mAh: Means milliampere/hour and refers to capacity, kind of like a fuel tank volume. It measures power over time and gives you an idea of run time for a given device. For example, a 5000mAh battery used on something that consumes 500mA continuous current, you can expect about one hour of run time (conditions affect run time).
Voltage: Nominal voltage for NiMH and LiPo battery cells are 1.2V and 3.7V respectively. Therefore, a NiMH battery with 7.2V has six cells. If a LiPo battery has 7.4V, it will have two cells. A LiPo battery with a voltage preceded by an ‘S’ value (e.g., 2S) refers to the two cells being in series, hence 2S or 3S, and so on.
C rating (LiPo only): This refers to the fastest a battery can be drained without damaging it. It’s a value to help you determine this, rather than the answer itself. The C rating multiplied by the capacity (in Amps, not milliamps) gives you the result.
The best way to explain is with an example. An RC car might have a continuous current draw of 60A and a burst draw (only used during acceleration, for example) of 100A. A 2500mAh LiPo battery with a continuous discharge rating of 40C and a burst discharge rating of 80C is more than enough to handle the 60A and 100A demands of the car.
Recommended RC car batteries
It’s best to stick with trusted names when it comes to batteries. Badly made ones can spell disaster for the device they’re connected to and can be downright dangerous. Also, check the dimensions of a battery to make sure it'll physically fit in your RC car.
There are a few different connector types out there. Tamiya and Traxxas have their own, so be wary of this when buying new batteries and chargers.
Voltz 4000mAh 2S 7.4V 50C Hard Case LiPo Battery Pack
Type LiPo | Connector type deans | Capacity 4000mAh | Voltage 7.4V | Cells 2 | Continuous discharge 50C | Burst discharge 100C | Dimensions 138 x 46 x 25mm
Voltz 2500mAh 7.4V 40C Hard Case LiPo Battery Pack
Type LiPo | Connector type deans | Capacity 2500mAh | Voltage 7.4V | Cells 2 | Continuous discharge 40C | Burst discharge 80C | Dimensions 138 x 46 x 25mm
Voltz 2400mAh 7.2V NiMH Battery Pack
Type NiMH | Connector type deans | Capacity 2400mAh | Voltage 7.2V | Cells 2 | Dimensions 135 x 45 x 25mm
Voltz 1800mah 7.2v NiMH Battery Pack
Type NiMH | Connector type Tamiya | Capacity 1800mAh | Voltage 7.2V | Cells 2 | Dimensions 130 x 46 x 23mm
Fconegy 3000mAh 7.2V NiMH Battery Pack
Type NiMH | Connector type Tamiya | Capacity 3000mAh | Voltage 7.2V | Cells 2 | Dimensions 134 x 46.5 x 24mm
Traxxas 11.1V 5000mAh LiPo Battery Pack
Type LiPo | Connector type Traxxas iD | Capacity 5000mAh | Voltage 11.1V | Cells 3 | Continuous discharge 25C | Burst discharge 50C | Dimensions 135 x 44 x 29mm
NiMH and LiPo battery charging
We know that NiMH batteries need to be fully drained before recharging, but the recharging process itself is pretty straightforward – many NiMH battery chargers have USB connectors. LiPo batteries are a bit fussier, requiring a constant current-constant voltage system and balancing. Balancing means keeping the voltage equal across all the cells in the battery.
The good thing is that many chargers are able to charge NiMH and LiPo batteries.
Etronix Powerpal Peak Plus
A popular charger, capable of NiMH and LiPo charging. You can select from 1, 3, and 5A charge current.
Etronix Powerpal Pocket 2 Lipo LiFe Balance Charger
A small and simple charger for two and three cell LiPo batteries. There is also a version for NiMH batteries.
Traxxas Dual 2S Completer Pack
Traxxas has its own connector types and therefore its own chargers. This set with two 7600mAh LiPo batteries and a dual charger sets you up completely for your Traxxas RC vehicle. Traxxas chargers are also wonderfully easy to use.