Nickel Metal Hydride (NiMH) and Lithium Polymer (LiPo) are the two main types of batteries used in the hobby industry. Generally, when you purchase a RC car, it is bundled together with a NiMH battery more often than not since it is affordable, reliable and safe in contrast to LiPo batteries.
Once you get used to running your car or buggy on a NiMH battery, you will inevitably move onto LiPo batteries however. Speedy charging, more punch off the line and more power during the charging process are a few of the critical factors that make LiPo batteries such a hit among the consumers.
RC Battery Abbreviations
LiPo – Lithium Ion Polymer (Type of battery)
NiMH – Nickel Metal Hydride (Type of battery)
NiCd – Nickel Cadmium (Type of battery)
mAh – Milliampere Hour (measurement of current over time) 1000mAh = 1Ah
Ah – Ampere hour (measurement of current over time) 1A = 1000mAh
A – Ampere (unit of current)
ESC – Electric Speed Control (connects the motor to the battery)
S – Series (commonly used in LiPo batteries, e.g. 3S means 3 cells connected in series)
V – Voltage (electric potential)
C – Capacity Rating (Also known as discharge rating, the higher the better)
Pros and Cons of NiMH batteries
- Safe to use
- Smaller increments in voltage
- Easy maintenance
- Large in size
- Lower energy density
- Not efficient
Pros and Cons of LiPo batteries
- High energy density
- Flat cell design
- High discharge rate
- Need to be handled with great care
- Need an ESC with LiPo cut off
- Need a balance charger
What battery do you have?
Each battery comes with a tag underlining its chemistry (NiMH or LiPo), capacity (mAh) and voltage (which is the multiple of 1.2 for NiMH and 3.7 for LiPo).
Appearance of NiMH batteries
A NiMH battery is a round shaped cell that is available on the market in different forms in accordance with varying applications.
Most of the NiMH batteries that are used to power RC cars consist of multiple Sub-C sized batteries as can be seen in the figure given below.
You guessed it right, yes! The typical AA batteries are just a single NiMH cell.
Outwardly, both NiMH and NiCd appear the same but have different chemical characteristics internally and so must be dealt with differently. NiCd batteries are not used anymore in the hobby industry. NiMH offer longer run times while the NiCd are adversely affected by the Memory Effect. This is why most of the electric RC cars out there make use of NiMH batteries instead of NiCd ones.
Appearance of LiPo batteries
A LiPo battery with a couple or more cells connected in series includes a balance lead. However, this is not a guarantee that it is a LiPo battery but it surely confirms that it is a Lithium battery. A balance wire is not required for NiMH batteries.
A LiPo battery cell is flat and rectangular in shape. There is no specific size for a LiPo cell. Majority of the RC cars are engineered to support a 6-cell NiMH battery with dimensions 137 x 45 x 234 mm. So, this tends to be the standard size more often than not.
Also keep in mind that some of the electric RC cars come with a rounded mount to support a 6-cell NiMH battery. In such a case, you can get a rounded hard case LiPo battery.
LiPos are available in varying dimensions which makes it easier for you to latch on to a battery that is in accordance with the dimensions of your car or any other application for that matter.
The voltage for a single cell in a LiPo battery is 3.7V so the voltages available are reduced. The two most common voltages for RC cars are 7.4V (2S) and 11.1V (3S).
- HPI 11.1V (3S) 3200mAh 35C battery inside a hard case rendering it reliability and durability
- A figure of Traxxas batteries with their different components
- A single cell LiPo used in iPhone 3GS
- HPI’s fire-proof LiPo safety pouch which is a recommended accessory when charging and storing LiPo batteries
You can find tons of information on the internet in addition to some conflicting suggestions which can be rather obfuscating. Memory effect related to NiCd batteries is a misconstrued concept particularly.
Voltage depression is a phenomenon that takes place in NiMH batteries but there is no authentic information if it can be identified. However, if you follow the below mentioned instructions, you can prevent it from taking place in your batteries.
NiMH tend to get charged only on chargers that provide support for NiMH batteries. The chargers compatible with NiCd batteries do not charge NiMH batteries. You will generally come across the question as to how long it takes for you to get your battery charged up.
One hour is a safe duration for majority of the batteries which implies that a 2000mAh battery can be charged at a maximum rate of 2A or 2000mAh. NiMH come in a couple of different forms. Trickle charger is the most common type since it is an affordable option. It is a charger with a low mAh output which does not stop charging once a battery has been charged completely but owing to its low output, no substantial damage can be done to the battery. Having said that, we recommend you to disconnect the battery as soon as it gets charged up. By dividing the battery capacity in mAh with the output of a charger, you can get the charge time for a charger. For instance, if a trickle charger has an output of 500mAh and the battery has a capacity of 2000mAh, you will get 2000mAh/500mA = 4 hours
This is a handy approach and uses more power than the Delta Peak method. Delta Peak is the other kind of NiMH charger.
The charger has the ability to identify when the battery has been charged to the fullest and stops charging. This implies that such a charger is able to charge a battery at a higher rate without overcharging a battery.
This is a safer approach to charging your battery and also informs you when the battery has been charged up completely.
As you use your electric RC car, you are actually discharging your battery. However, you can also discharge your battery using a smart charger.
It is important that you do not completely discharge your NiMH battery in order to ensure its longer lifespan.
It is ideal to store a NiMH battery at room temperature in a dry location.
Make sure that a battery does not get heated up since this can reduce its lifespan significantly.
It is prudent to get your NiMH battery charged up before storing it. Also, it is important that you charge it frequently (every 7 to 30 days) which assists the battery in getting discharged at a rate of 1% per day. So, if you leave your battery uncharged for 4 months, it could damage it beyond repairs.
Having said that, this is not an issue that is related to Low Self Discharge batteries.
NiMH are recyclable!
Typically, NiMH are safer as compared to LiPo batteries, however, if used in a wrong manner, you still can end up damaging them. Let’s go through some of the Dos and Don’ts to keep your NiMH batteries in the right shape.
Do charge in a safe, open area.
Do use a smart charger.
Don’t leave a battery charging unattended for longer periods of time.
Don’t charge on a charger that is not designed for NiMH batteries.
Don’t charge over 1C.
Don’t discharge the battery completely regularly.
Don’t drop your NiMH batteries as they can get damaged.
LiPos need to be handled with care as opposed to NiMH batteries. Here are a few things that you need to do right in order to ensure that your LiPo batteries perform efficiently and boast a longer lifespan.
As soon as you get a LiPo battery, get it charged up. Ensure that the charger is compatible with the battery. You can check it out from the instructions scribbled on the charger, packaging or the instructions manual.
Once you are sure that the charger is compatible with the battery, get the battery charged up. In case of a programmable charger, apply the correct settings to charge your battery.
For instance, if we are looking to charge the HPI LiPo 11.1V 3200mAh on the iMAX B6AC V2 charger, it will need to be configured to LiPo charge with a charge rate of 3A and a voltage of 11.1V (3S). This is similar to most of the chargers with a similar software.
So, the charging rate should be set to 3.2A as it will take an hour to get a 3200mAh battery charged up at this rate.
This is the general rule for most of the LiPo batteries.
This is the 1C rule which implies that you can charge a LiPo battery at the same rate as its capacity which is 3.2A here. A battery with 5200mAh capacity can be safely charged up to 5.2A.
Discharging or C Rating
In order to ensure that the battery is able to furnish the requisite power for your electric RC car, you need to take a look at the battery’s C (Capacity) rating. This rating generally lies between 10 and 90 C. Suppose, we are using a 3200mAh 11.1V 35C LiPo battery. This implies that we have 3200 x 35 = 112A. This means that if your car has an 80A ESC, this will inform you that the battery can manage more than the ESC will deliver; thereby making it a safe rating for the car.
LiPo need to be stored well in order to ensure their efficiency and longer lifespan. If a LiPo battery is stored flat or completely charged for more than a couple of weeks, it will be detrimental to the lifespan and performance of the battery.
All LiPo batteries should be stored at 3.7V to 3.85V per cell which is about half to three-fourths of being fully charged.
If your charger comes with the storage charge setting that automatically charges or discharges the battery to requisite storage voltage and you are sure that the battery will not be used for more than a week, then opt for the storage charge setting.
If your charger is not equipped with this feature, then you can charge it for half of the charging time. This should provide the battery the requisite voltage which is preferable to storing the battery flat or completely charged up. You can also check the voltage of the cell using the balance lead and the multimeter.
If your battery has been damaged or does not get charged anymore or is unusable, you have to dispose it off. You should not put it in the dustbin since it will still be dangerous.
Get the LiPo battery completely discharged before disposing it.
Connect a device that has a low current draw such as a light bulb and get the battery discharged. The time of discharging will depend on the extent of battery’s charge percentage but generally it will take two to three days for the LiPo to get discharged completely.
We suggest you to play it safe with LiPo batteries since there are lots of horror stories related to LiPo batteries. They can catch fire if being mishandled. There can be a number of reasons for the LiPo batteries to catching fire but over discharging or overcharging are two of the most common factors.
By using a LiPo balance charger, you can reduce the probability of damage to the battery and its surroundings. Never ever use an ESC without a LiPo cut-off feature.
A LiPo safe pouch should always be used while charging and storing these batteries. Ensure that once you store them, the requisite cell voltage is maintained.
More and more devices such as laptops, smartphones, power tools etc. are using batteries as their primary power source. It is quite common to use a battery in your everyday chores.
So, it is important that we are well aware of how to manage and use batteries in order to ensure safety, longer battery lifespan and high performance.