Written: 2009-08-20
Last edit: 2009-09-16

- What you should know about LiPo Batteries -

Version française

Words: Donald Natale, Add-on*: Arn0
Photos: Courtesy of Team Associated

What everyone should know about the Use and Care of Lithium Polymer (LiPo) batteries.

What size of voltage battery should I use, 3.7, 7.4 volts, 11.1 volts or higher?

Be sure to check your ESC's (electronic speed control) allowed voltage input from the specifications in the supplied manual that you received when you purchased the speed control. Remember higher voltage means the motor can generate more speed however; the more heat is also produce.

What is the difference between a one, two or three cells lipo battery?

The primary difference is voltage! A single cell or (1S) Lipo is 3.7 volts, 2-cell or (2S) Lipo is 7.4 volts; 3-cell or (3S) is 11.1 volts.
I am sure you have figured out, each cell is 3.7 volts and depending on how many cells you have in series you can multiply those numbers by 3.7 and that will give you the packs voltage. (Example 3 x 3.7 = 11.1) Running a 3-cell Lipo battery will give you the relative equivalent voltage if you were to run 9 to 10 NiMh or NiCad type cells that are 1.2 volts per cell. Electric motors are capable of running different amounts of voltage.
However, it is important that you pay attention to gearing; incorrect gearing with prolong runs from high capacity batteries can results in excessive heat to the motor and the battery. If you are not careful, it is possible the battery could overheat which will cause it to swell and possibly catch on fire or explode be sure to check for proper gearing no matter what motor you run, brushed or brushless.

What does the C rating mean on Lipo batteries, example: (10C, 20C, 35C etc.)?

“C” rating is the allowable amp draw of the battery. It relates to discharge limits of the Lipo battery. The higher “C” number means that the battery is capable of taking a higher discharge load without causing damage to the battery.
There is no real industry standard on testing for the “C” rating and each manufacture test determines what the “C” rating will be for their batteries based on their findings. It is possible to buy two batteries by two different manufactures with the same “C” rating the batteries will have completely different performances.

I see 180mah, 2000mah, 3600mah, ect. What does “mah” stand for?

MAH is the (Milli Amp Hours); this is the capacity or run time of the battery. The higher the milli amp capacity 2000, 3600 and so on equates to how much run time the battery will have. Be sure that you check the motors temperature during the first run for proper gearing. Incorrect gearing will over heat the motor and could cause irreversible damage.

What is 2S2P!

2S2P...Means there are two cells (2) in series (S) (which makes 7.4 volts) and two (2) in parallel (P) to get capacity. If you were to add another cell in series that would increase the (S), number to and would raise the capacity from 7.4v to 11.1v at that time you would have a 3S2P battery, and that number can increase even more depending on how many cells are added to the pack.

I see batteries on the market and some say TX or RX even though they may have the same specifications.

TX = (Transmitter) and RX= (Receiver) each uses different voltage batteries. Typically, an RX 2-cell is no more than (7.4 volts) and TX is (11.1 volts)... plugging in a11.1-volt battery into your RX could cause a catastrophic failure unless you have a voltage limiter also connected. Depending on the specifications of your receiver, you may need to run a voltage limiter with your RX when using higher voltage battery, a typical RX runs up to 6.0 volt, but that does not mean you cannot use higher voltage batteries, just be sure to check with the manufacture on the receiver’s capabilities.

Do I need to balance my Lipo batteries?

YES, if the battery goes out of balance they have higher chances of failure since the packs are sensitive to overcharging and discharging. Your Lipo battery pack will have either a balancing port or a balancing connector; you may need to purchase an optional balancer like the (LRP Precision Parallel LiPo Balancer #LRP45200) unless your charger is capable of balancing Lipo batteries as well as charging them.

NOTE: A balancer keeps the voltage in your cells equal, which helps to keep the battery from over discharging or overcharging and helps produce the best performance from the battery. Using a balancer during the charge sequence is very important, overcharging a cell can cause it to spontaneously swell and quite possibly explode. A balancer will remove this risk factor however, as with anything Lipo, so take caution and read the manufacture usage instructions before using your battery.

Do 3-cells or more take more time to maintain?

Nope, it does not take any more time to maintain any size lipo battery is just common sense and that is your greatest tool. Unfortunately, people who do not take care and follow the rules set by the battery manufacture are to blame for Lipo related disasters due to incompetence.

A voltage limiter or voltage cut-off, is this needed in Lithium Polymer applications?

The limiter is actually a voltage cut-off specifically designed so you can use Lipo type batteries with older receivers and speed controls that are not Lipo compatible. When using Lipo as a receiver pack or when using Lipo batteries with older version speed controls, it is to prevent the battery from discharging to low during use. The cutoff is usually around 6.25v or 3.125 volts per cell. Once a Lithium Polymer battery discharges below 3.0 volts per cell, there is less likely chance that you will be able to get it to recharge again.

Storage: If you do not plan to use your lipo pack for longer than a week, store it at 50-60% of the pack’s rated capacity. Make sure to cycle and/or balance your packs at least once per month since leaving them on the shelf for a prolonged period can cause the packs to get severely out of balance or even go dead.

Lithium Polymer Safety Tips: Lithium Polymer cells are a tremendous advancement in battery technology for RC use however, due to the chemistry makeup of the lithium cells; there is a possibility of fire if not used properly! It is unavoidable due to the nature of lithium itself (see details). This is no different from many things we use in daily life – knives, kitchen cleaners, automobiles, for a few examples – which are inherently dangerous but which can be and are used safely by adhering to simple rules and precautions.

Example: It is best not to run motors until they reach 100 degrees Centigrade or 212 degrees Fahrenheit this could damage and could cause a battery to overheat. On the other hand, by overcharging the battery with incorrect charger settings, and or by over discharging the battery…Each of these scenarios can be the cause of a battery failure!

Charging Precautions:
• Be sure that Lithium Polymer charger settings are correct for the battery pack being charged – both voltage and current settings.
• Lithium Polymer should be CHARGED and STORED in a fire safe box or Lipo Sack for added safety.
• Do not charge batteries near flammable items or liquids.
• Keep a dry fire extinguisher nearby - or a large bucket of dry sand, which is a cheap and effective extinguisher.
• Never, charge inside an automobile even when parked.
• Batteries should NEVER be left unattended while charging.
• KEEP BATTERIES AWAY from children and pets at ALL times.

Handling Precautions:
New cells may have a high initial charge and care should be taken to insure that battery is not short-circuited.
• Never, leave batteries on a hot day in direct sunlight, or in any other place where ambient temperature may exceed 140F / 60C.
• Do not put the loose cells in a pocket, bag, or any conductive surface were the tabs could become shorted.
• Take care that metallic objects like hobby knives do not puncture the cells
• If the electrolyte in the cells should get on your skin, thoroughly wash with soap and water. If in the eyes, rinse thoroughly with cool water. Immediately seek medical attention for this.

Should I try to fix a Lithium Polymer battery that has been damaged?

Lithium Polymer batteries that has become damaged by puncture or over discharging or by over charging beyond the recommended limits and the pack has sings of leaking or swelling, it is NOT RECOMMENEDED that you try to fix or repair the battery.
It would be best to follow the list below for proper disposal of the Lipo cells. The batteries must also be cool before proceeding with disposal instructions.

To dispose of Lipo cells and packs:

1. If a Lipo cell in the pack has been physically damaged, resulting in a swollen cell or a split or tear in a cell’s foil covering, do NOT discharge the battery. (Proceed to step 5 on this list.)

If you are disposing of Lipo batteries/cells:

2. Place the Lipo battery in a fireproof container or bucket of sand.
3. Connect the battery to a Lipo discharger. Set the discharge cutoff voltage to the lowest possible value. Set the discharge current to a C/10 value, with “C” being the capacity rating of the pack. For example, the “1C” rating for a 1200mAh battery is 1.2A, and that battery’s C/10 current value is (1.2A / 10) can be used; a power resistor or set of light bulbs can be used as long as the discharge current does not exceed the C/10 value and cause the cells to overheat. For Lipo packs rated at 7.4V and 11.1V, a 150-ohm resistor with a power rating of 2 watts (commonly found at a local electronics store) can be connected to the pack’s positive and negative terminals to safely discharge. Connecting the battery to an ESC without a Lipo cutoff setting and allowing the motor to run a low RPM until no power remains would be an alternative way to discharge the battery.
4. Discharge the battery until its voltage reaches 1.0V per cell or lower. For resistive load type discharges, discharge the battery for up to 24 hours.
5. Prepare a plastic container (do not use metal) with normal tap water and mix in 1/2 cup of salt per gallon of water. Drop the battery into the salt water. This container should have a lid, but it should not need to be airtight. Allow the battery to remain in the tub of salt water for at least 2 weeks.
6. Remove the Lipo battery from the salt water, wrap it in newspaper or paper towels and take to reputable battery recycling center here is a link for centers in the US (http://earth911.com/) and if one is not available you can place it in the normal trash. Since they are now landfill safe after completing the steps listed above.

Don Natale
Senior Customer Support
Team Associated

*Add-on = Lithium link