Batteries are such an indispensable part of RC models that they can make all the difference between fast and sluggish toys. As an RC hobbyist, you have two battery options to choose from; Nickel-Metal Hydride (NiMH) or Lithium Polymer (LiPo) batteries. But, when it comes down to picking one, which type gets the crown?
In this comprehensive article, we've put together everything you need to know about LiPo and NiMH batteries. From their performances, safety features, and looks, you'll find all the differences between LiPo and NiMH batteries here.
Let's dive into RC battery tech!
What are LiPo batteries?
A LiPo battery is a rechargeable battery that uses lithium-ion technology and a polymer electrolyte. Many hobbyists use these packs to power their RC models as they are one of the most popular around. Out of the RC industry, gadget-lovers have also found them useful.
LiPo batteries are tweaks of Lithium-ion and Lithium-metal battery packs. They didn't get into the battery scene until the 1970s when manufacturers decided to try out a different ion-containing substance called electrolytes.
In a pack, you'll find rectangular single-cells connected in either series or parallel. When fully charged, these cells have a voltage of 4.2v and a resting voltage of 3.6 or 3.7v. However, there are High Voltage Lithium Polymer (HVLi) cells that can be charged to a higher value. Often, the voltage of HVLi cells can peak at 4.35v.
The number of LiPo cells and how they are arranged in a pack are described by numbers and figures. For example, the most common type for RC racing are 3S, 4S, and 5S packs. A 4S pack means that there are four cells arranged in series.
On the other hand, you could also find batteries that are described as 2S2P. This means there are four batteries: two arranged in series and two connected in parallel.
How do LiPo batteries work?
LiPos work on the same principles as lithium-ion cells called intercalation and de-intercalation. For these processes, you'll need:
- A positive conductor of electricity (electrode)
- A negative electrode
- A liquid-like substance called an electrolyte
The positive and negative electrodes give off and receive ions, while the electrolyte serves as a medium for these ions to move.
Your LiPo battery charges when lithium ions move from the positive end to the negative end through the electrolyte. On the other hand, it discharges when lithium ions move from the negative electrodes to the positive ones.
This implies a battery fast-charges or discharges quickly when it sends ions to the other electrode in a blink.
What are NiMH batteries?
NiMH batteries are also rechargeable batteries, but they are packed with cylindrical cells. Generally, ready-to-run (RTR) RC models come with this battery type in the box, and they provide the power hobbyists need to use their gadgets.
NiMH cells are variants of Nickel-Cadmium cells (NiCd), with only a few differences to set the two batteries apart. And like LiPos, research into NiMH batteries started around the early 1970s. Since then, they've evolved from being just another battery type to one of the top packs to power gadgets and devices.
These battery packs are usually available in AA batteries. However, there are also AAA NiMH batteries. Generally, each cell operates at 1.2v, which is enough to power different types of devices.
How do NiMH batteries work?
Unlike LiPo batteries, the working principle of NiMH batteries involves chemical reactions. Each cell consists of:
- A positive electrode made of a substance called nickel oxyhydroxide
- A negative electrode called metal hydride that stores hydrogen
- A liquid-like solution called the electrolyte (often potassium hydroxide)
When your battery charges, extra electrons move into the negative electrode, and the opposite happens when your battery discharges.
NiMH vs. LiPo: Which battery is better?
As we've established, NiMH and LiPo batteries have their advantages and disadvantages. However, what is the dividing line between them?
- Differences in performance: An RC battery's performance is the top decider of who wins a race. Therefore, if you've got a pack that delivers high punch, runs for long hours, and sustains its voltage, you'll have a competitive edge.
LiPos: LiPo battery packs generally have high voltages and capacities. With this advantage, they allow much speed and power to RC motors and are super-fast during speed tests. This makes them ideal for RC racing.
NiMHs: On the other hand, NiMH packs don't have the voltages and capacities of LiPos. For example, a typical NiMH battery comes in 7.2v (6cells), but you can have a 7.4v LiPo (2 cells).
This implies that NiMH packs don't provide as much power or punch as LiPos.
- Differences in lifespan: Most batteries come with warranties. However, these warranties usually don't run past the battery's lifespan. If you want to have any chance of enjoying any battery for years, you'll need to know how long you can expect to use one.
LiPos: The shelf life of a regularly used battery pack is two to three years. If you follow the book on how to use one and abide by all safety precautions, you could also get a few months on the expected lifespan.
In terms of charge cycles, you can expect LiPo batteries to last for 300 to 350 cycles. After this period, the packs don't completely fail but only hold about 80% of their charge.
LiPo batteries begin to age from their first use largely because of the near-perfect charging process and its electrolyte deteriorating.
NiMH: These batteries have about the same shelf life as LiPo batteries. In terms of charge cycles, many manufacturers claim that their NiMH packs can last for 700 to 1000 cycles.
Of course, these figures depend largely on an enthusiast's care for and use of the batteries in their RC models and devices.
- Differences in cost: On the off-chance that you don't want a LiPo and NiMH pack, how do you decide which battery type to go for?
One way out is to look at the price that both batteries go for.
LiPos: Compared to other battery types, LiPo packs are a tad more expensive. However, with the features they bring to the table, it is understandable that these packs go for a few bucks to hundreds of dollars.
The materials used to manufacture LiPo batteries add to the cost of each pack. Also, the increasing demand for these batteries and the extensive tests they undergo make the overall cost go up.
NiMHs: NiMH batteries are easier to manufacture and maintain. Hence, they are the cost-effective option between NiMH vs. LiPo. For some manufacturers, the cost of producing a NiMH pack is about 75% less than that of LiPo packs.
NiMH batteries have quite some development and regulatory steps. However, they are nothing compared to the extensive tests that LiPo batteries have to undergo.
- Differences in charging and discharging settings: LiPo and NiMH batteries aren't single-use packs. With a good charger, you could get them fully charged again.
Discharging is simply using your RC device or electronic gadget.
LiPo: One of the first things you'll need after getting a LiPo battery is a compatible charger. LiPo's don't work on NiMH chargers and vice-versa.
Next, you need to pick charging settings to use with the battery. The batteries don't have the memory effect. So, you don't need to discharge them before plugging them into a charger.
LiPo chargers monitor each cell to ensure they all have the same charge. The charge rate of a pack is graded in ampere or milli-ampere per hour. Generally, this rate should be proportional to the battery's capacity.
For example, if you have a 3200 mAh battery, then the safe charging rate to set on the charger is 3.2A. This is known as the 1C rule.
Overcharging a LiPo battery can damage the cells by making them expand rapidly. In turn, this will reduce the lifespan of each cell.
The C rating refers to the discharge setting of a LiPo battery pack, and it should be higher than that of your RC model. Charging a fully-charged LiPo battery while it discharges (trickle-charging) can damage LiPos or any other Lithium-ion battery.
NiMH: As we've established, a NiMH battery only works with NiMH chargers.
With these batteries, it's also safe to use the 1C rule. For example, if you have a four-cell NiMH pack with a capacity of 3000 mAh, then it's safe to charge it at a maximum rate of 3 amps.
NiMH chargers have two different styles: the Delta-peak method and the trickle-charge method.
Trickle charging a NiMH battery means charging it at a low ‘mAH’ continuously, even when the battery is full. Since it's done at a low charging rate, the supplied current won't damage the battery cells. To calculate how long it takes to trickle-charge a NiMH battery, simply divide the charger's output rate by the battery's capacity.
The second method (Delta-peak) notifies your NiMH battery when the pack is full and charging stops.
You shouldn't overcharge a NiMH battery.
- Differences in safety and disposal: Batteries are generally safe to use in RC models and other devices. However, you need to maintain them to avoid dangers like explosions and fires.
LiPo: One thing to note about LiPo batteries is that they aren't designed to be stored when fully charged. Instead, you should keep them at their nominal voltage (3.7 to 3.85v), which implies 50% to 70% charged. This way, you'll preserve the cycle life of each cell while still enjoying the punch they deliver.
When you want to dispose of a LiPo battery, you'll have to completely discharge it to prevent fires and explosions. To do this, you can connect a low-draw device to the battery until it’s completely depleted. How long you have to wait will depend on the capacity of the battery.
LiPo batteries are unsteady, and you should dispose of them immediately they can't hold a charge. To prevent damage and other mishaps, ensure you:
- Use a balance charge with a LiPo battery at the right setting
- Use an Electric speed control (ESC) with a LiPo cut-off.
NiMH: With NiMH batteries, your best bet is to not completely discharge each cell in a pack. If you do (perhaps to make them last longer), you could get the opposite effect and shorten their life span. That's because completely discharging a multi-cell NiMH battery can reverse the cells' polarity and permanently damage them.
Instead, you should store NiMH batteries dry at room temperature to prevent them from heating up. Charging a pack before storing helps because NiMH packs self-discharge 1% current when not in use. And after they've spent their lifespan, you could either dispose or recycle them.
NiMH batteries are generally safer than LiPos, but they also need some maintenance. Try not to drop them because these packs are greatly affected by shock.
- Differences in weight: Every hobbyist faces the capacity-weight tradeoff when getting a battery pack. This means if you find a high-capacity battery, it'll likely be heavier than a lower-capacity pack.
Lighter packs make RC models easier to move and lifting electronic devices a breeze.
LiPo: Since they don't have metal cases, LiPos are lighter than most battery alternatives. For most RC hobbyists, this quality is the top-selling point of the battery type.
NiMH: NiMH batteries are heavy primarily because of their metal exterior. They are also bigger in size than LiPo batteries.
- Differences in appearance: Firstly, every pack should have a description that tells you exactly what type of battery you have. You should also find technical specs like the capacity and voltage on the label.
LiPos: The easiest way to spot a LiPo battery is in its shape. These packs have box-like designs with two or more cells. There's no standard size for each cell, and the dimensions can vary in length, weight, and height. Nevertheless, their lengths of LiPos are often bigger than other dimensions to fit the elongated space for them in RC models.
Another thing you can use to pick out a LiPo battery is the presence of balanced leads. With one, each cell in a LiPo charges to full capacity.
NiMHs: These batteries, on the other hand, often have penlight cells in each pack. They could be arranged in a circle to fit small RC models, laid out on a row, or connected with a hunch.
NiMH batteries don't have balance leads because the cells level out and charge equally.
Applications of NiMH and LiPo batteries
- RC toys: LiPo and NiMH batteries are used extensively in RC equipment. From RC planes, drones, cars, trucks, boats, and buggies, these batteries can fit different RC models. You only have to find the pack that matches your voltage and capacity requirements.
- Consumer electronics: Other devices that you can find LiPo and NiMH batteries include power banks, laptops, smartphones, and electric cigarettes.
- Electric vehicles: Reputable car manufacturers like Hyundai Motor Company use LiPo batteries in their cars. However, NiMH batteries are more popular in electric vehicles. In truth, first-generation hybrid vehicles like models from Toyota and Honda used NiMH batteries.
Recent advances in NiMH vs. LiPo batteries and what they imply for RC enthusiasts
For many RC hobbyists, the ultimate goal is to have a long-lasting, massive-capacity battery that weighs only a few ounces. While researchers and scientists haven't achieved this yet, several advances have been made.
With NiMH and LiPo batteries, these discoveries have been linked with prolonging each battery’s life.
NiMH discoveries: As we've established, NiMH batteries have long cycle lives, but they don't last a lifetime. However, researchers at Stockholm University have found a way to multiple the lifespan of these battery packs. This implies that they can take on more charging cycles without losing their capacity. The discovery also means that NiMH can be restored when they begin to wear out.
From the study and previous discoveries about NiMH batteries, the researchers developed a new metal hydride surface structure. This structure combined the alkaline etching of hydrogen with controlled oxygen.
This discovery is one of the most recent ones to-date. However, there've been several other advances in NiMH battery performance.
While battery manufacturers haven't started adopting these new technologies, NiMH could well offer identical benefits as their LiPo counterparts.
LiPo discoveries: Advances in LiPo batteries have been in line with all packs that work on Lithium-ion technology.
In recent years, the development of high-voltage LiPo batteries has been the most notable of them. The batteries have a nominal voltage (standard operating voltage) of 3.8 volts per cell. Therefore, a two-cell high voltage LiPo pack will have 7.6v per pack instead of 7.4v per pack.
High voltage LiPo batteries offer more power, but for only a short period. You can use them on any ESC that is set up for LiPo packs. With these batteries, you'll also get more runtimes than in standard-voltage LiPo batteries.
HV LiPo batteries require a special charger or one that allows you to bump up the voltage past 4.2v. Luckily, new LiPo chargers come with this feature.
Manufacturers have started producing HV LiPo batteries. Despite their advantages, these packs haven't proven themselves in RC races. They could well be the next generation of LiPo batteries but need to be put to more tests.
Q1. Are the safety precautions for LiPo batteries the same for NiMH packs?
There are general steps to take for any battery pack you get for your RC toy or electronic device. However, since LiPo batteries are highly flammable and typically more hazardous than NiMH packs, you should take extra care when using them.
You can safely use LiPo batteries by minimizing their exposure to conditions that affect their lifespan.
Q2. Do NiMH and LiPo batteries have the 'memory effect'?
LiPo batteries don't have the memory effect. However, this concept can be observed in NiMH battery packs.
This means nickel-metal hydride batteries lose their capacity when repeatedly recharged after they are used for a while. The packs seem to remember the small capacity.
Q3. What is the difference between NiMH and LiPo in Airsoft?
LiPo packs are small and light. Therefore, they are the standard for the sport of Airsoft. Asides from their weight, they also offer more performance than NiMH packs.
7.4v LiPos provide the same performance as 8.4v NiMH battery packs.
Q4. Can you fast-charge a LiPo and NiMH battery pack?
You can fast-charge LiPo batteries. For LiPo batteries, ensure you use a balance charger. Else, some cells will have a higher charge than others.
Not every NiMH battery can be fast-charged. If they can, ensure you use the correct charger. While a NiMH charger will work on NiCd packs, a NiCd charger will overcharge NiMH packs.
Q5. Which battery type has a higher energy density?
A LiPo battery has a higher energy density than a NiMH pack. The energy density of a battery is directly proportional to the runtime. Therefore, packs with high energy densities run for longer hours than those with small energy densities.
For a long time, LiPo and NiMH batteries have gone head-to-head. There are a number of factors that set these batteries apart, but they both have the same use: to power devices, especially RC models.
Whether you're an RC enthusiast, veteran, or just tech-lover, you'll need to know the differences between NiMH and LiPo batteries to choose a battery pack over the other. We hope we've cleared the air on everything you should know about these batteries.
Ultimately, LiPos aren't better than NiMH or the other way round. Depending on your needs, you could pick any battery type when you've got to choose one.