RC Battery Guide
Posted by RC Hobbies Outlet on 21st Feb 2020
Being a RC vehicle hobbyist will teach you how to maintain and care for your vehicles.
Hobbyists are automatically drawn towards taking care of their vehicles to keep them lasting long and performing at their best. Which means gaining some knowledge of underlying electronics, batteries, mechanicals, cleaning and some plain old elbow grease.
As you play around and grow your RC collection you will learn about how your vehicle operates and this knowledge will improve your RC maintenance and operation skills.
One of the very fundamental aspects of maintaining and taking care of your electric RC vehicle includes understanding batteries
As you may have already read or heard about, there are two main battery types used in most electric RC products; Nickel-Metal Hydride (NiMH) or Lithium Polymer (LIPO) batteries.
Before we further discuss the details of choosing either battery, lets learn a few key terms for RC batteries. Battery Capacity refers to milliamp-hour or mAh. The higher the mAh, the longer your battery will last before a full recharge is required.
All in all, a higher capacity equals to longer run time for the battery. For example, a 5000 mah battery will run your vehicle about 2.5 times as long as a 2000 mah battery, before you need a recharge.
Voltage refers to how much power/speed the battery can deliver. In general, the higher the voltage the higher the vehicles top speed. Although, all RC vehicles come with a designated amount of voltage they can handle before the vehicle can get seriously damaged. The voltage your RC can handle is largely determined by your Electronic Speed Control (ESC) specifications and to a lesser degree by the motor.
The voltage of a battery is determined based on how many cells are included in each battery pack and what kind of battery is being used. NiMH batteries carry 1.2 volts per cell, and generally a NiMH battery pack includes 6 to 7 cells. LIPO batteries carry 3.7 volts per cell, and hence a lesser number of cells is required per battery pack, and most LIPO battery packs include 2 – 4 cells in a pack. LIPO batteries are sometimes specified by #S -- for example a 3S battery would be 3 cells and have a voltage of 11.1v.
NiMH and LIPO Batteries
Now that we know some battery lingo, let’s get to know the two different battery types.
LIPO batteries are known to have higher energy density in smaller packages. Compared to NiMH batteries, LIPO batteries are lighter and have a much higher surge/discharge capacity, so they can deliver the bursts of energy that are required during acceleration and when driving through resistive surfaces. LIPO batteries maintain their voltage longer as the battery discharges, compared to NIMH batteries where the voltage drops more quickly.
LIPO batteries have an additional rating called C – which defines the discharge rate or surge capacity of the battery – both continuous and 10 second burst rating. A rating of 25 - 30 C is fine for most RC brushless electric vehicles, although higher C ratings can be used as long as they do not exceed what the ESC can handle. This is only of concern if you are using a battery voltage at the top of your ESC range and you are driving through a resistive surface such as heavy grass. Your brushless ESC will increase the discharge demand on the battery, and in the case of a high C battery, the surge could exceed the capacity of the ESC and motor.
Overall, LIPO batteries are lighter than NiMH batteries of similar voltage and capacity, but are also more expensive. They do offer your vehicle more robust power as they are able to maintain voltage for longer before the battery pack is completely discharged.
With time LIPO battery technology has become much safer to use, however some special care is still required. Some precautions and LIPO care practices include:
- Do not allow LIPO batteries to discharge bellow 3v per cell or the battery may become damaged (most brushless ESCs have a low voltage cut-off at this level).
- Protect the LIPO battery from physical damage or punctures and avoid use/charging if it is physically damaged. LIPO batteries with a hard case are better protected from damage, but soft packaging can also be used if the battery case in the vehicle provides protection.
- Use a balanced charger (or balanced mode) when charging, which ensures that all cells are charged to approximately the same nominal voltage and hence perform the same when they are at full charge. LIPO batteries normally come with a white separate connector for charging.
- If you are not using your LIPO battery for several weeks, to maximize the life of the battery it should be stored at 50-70% charge. One way to do this is fully charge the battery and if your battery normally lasts 30 minutes – drive your vehicle for 10 minutes (you can adjust this time depending on how long your battery lasts) – which should put the charge under 70%. Alternately, if the battery is almost fully discharged, you can charge for 50% of the time it normally takes to charge. If you store the battery when it is completely or almost discharged, or fully charged, the battery may be stressed or damaged. We would also recommend you store the battery in a cool dry location and you may also want to store it inside a LIPO storage bag.
And finally, do not use a LIPO battery if it has started to swell.
On the other hand, NiMH batteries are known to be ultra-safe, easier to use and charge, and normally have a longer charge/discharge cycle life. These are better suited for brushed motor vehicles, as they are often unable to handle the surge requirements of brushless motor RC vehicles. NiMH batteries are also the more economical choice for brushed motor vehicles.
NiMH batteries can charge quickly and the discharge rate is fairly linear, so while running your vehicle it is a fairly constant drop in the charge of the battery. These batteries are comparatively less expensive and do not require a lot of special care unlike the LIPO batteries. However, they do not offer the same robust power, as your vehicle will run slower and slower with time as the battery discharges.
If you are not using your NiMH battery for many weeks, it can be stored with a partial or full charge.
Brushed motor vehicles can technically handle both NiMH or LIPO batteries if they are around the same voltage, however you need to ensure the ESC has the low voltage cut-off required for LIPO batteries. Most HSP brushed motor ESCs have a strap setting that can be changed if you are using a LIPO battery. If you use a LIPO battery with a brushed motor ESC that does not have explicit support for LIPO batteries you could damage your battery.
Additionally, many brushed motor vehicles use a white Tamaya connector, and as most LIPO batteries come with a different connector, you will likely need an adapter if you want to use a LIPO battery.
For both NiMH and LIPO batteries, we would recommend disconnecting the battery when you have finished using your vehicle. Sometimes ESCs can continue to drain power from the battery even when the vehicle is turned off.
Charging and Safety
First and foremost, when charging any battery, make sure to charge away from any flammable materials and never leave the battery unattended while charging. This is especially important when using a high-speed charger with a LIPO Battery, -- ensure you have the charger and battery placed in a safe spot. Overcharging a battery can also lead to malfunction or even a fire, so make sure to follow the manufacture’s direction or when in doubt follow the 1 C charge rule mentioned below.
The general rule of thumb while charging LIPO batteries is to keep the charge rate at 1 C. If you are missing the manufacturer’s instructions for charging then follow the 1 C rule, especially for LIPO batteries. This rule recommends that you charge the battery at one times the capacity of the battery in amps. For example, a 5000 mAh battery should be charged at 5 amps or less, to minimize stress on the battery.
When charging NIMH batteries with a fast charger, we have found that the battery may not fully charge if you are charging at a rate greater than 2.9 amps
There are battery chargers that will enable a faster battery charge but you also have to keep in mind this will cause wear on the battery, which may lead to faster deterioration of your battery. Although on the flip side, you can be back to having fun with your RC vehicle faster, with a faster charger. However, never use the incorrect charger for your battery type, as it can also prove to be unsafe.
For more tips, tricks and guides, check out our other blogs. As always, for any questions reach out or comment below.