Batteries Part 1 – Battery Handling

Extracting the longest service life out of a battery packs is of prime concern. ​
One of the key factors contributing to the service life is correct storage.​

The greater portion of the service life of many battery packs is spent in storage. The conditions that a battery pack is exposed to during storage directly impact on the achievable service life from the battery pack.​

Additionally a unique characteristic of Li-Po batteries is that their life span is dependent on aging from time of manufacture, not just a number of charge/discharge cycles. An older battery will not perform as well as a new one, due solely to its age.​

This limitation is not widely publicized, and consequently is not well known:-​

As a Li-Po battery ages, it’s internal resistance increases.​

Under load the effect of internal resistance is to cause the battery terminal voltage to drop, which in turn reduces the maximum current that the battery can provide to the load. To add to this phenomena – as Li-Po batteries age, usable capacity is lost​

A fully charged Li-Po cell will produce a terminal voltage of approximately 4.2 volts. Li-Po’s are different from other battery chemistries as they should never be stored fully charged. In fact, LI-Po batteries should be stored approximately “half full”, or at 50 State of Charge (SoC).​

Many of the newer Li-Po battery balance chargers include a “Storage Mode”, which charges the pack to the proper reduced voltage state for storage purposes.​

Some commercial chargers charge cells to 3.85Vdc in Storage Mode. ​

Storing battery packs at the proper voltage level is the simplest thing you can do to lengthen their usable life span (assuming of course proper application).​

‘Storage’ should not only be considered as a long term, e.g., “over the winter” situation. Even if, for example, you only fly on weekends, these battery packs are technically in storage all week – week after week – during the entire flying season. Those cumulative hours can add up slowly degrading the battery packs.​

Li-Po batteries produce energy via a chemical reaction that occurs inside sealed foil envelopes. The output power is produced by a chemical reaction. The aging/degrading process is also in reality a chemical reaction.​

A chemical reaction doubles its speed for every ten degrees increase of ambient temperature.​

It is for this reason that Li-Po batteries do not perform as well in cold weather. Cold “slows down” the chemical reaction process – something we need to be aware of when anticipating aircraft performance.​

Reducing storage temperature slows the chemical reaction of the aging/degrading process, however there is a limit as to how cold is acceptable. Li-Po batteries should not be for example frozen solid. Laboratory testing has determined that the typical household refrigerator (0 to +5 degrees C) is the perfect storage place.​

Li-Po battery packs should be placed in plastic zip top storage bags prior to placing them in the refrigerator for storage. When removed from the refrigerator prior to use, leave the batteries in the zip top storage bag to prevent any atmospheric moisture from condensing on them as they warm. After the batteries have attained room temperature, that may be used as normal. ​

Permanent Capacity Loss versus Storage Conditions​

There have been very few cases of batteries suddenly exploding when they are not being used, abused or charged (i.e. during transport and storage).​

Lithium batteries are commonly air-freighted protected by a few layers of bubble wrap and small versions are carried around in mobile phones. Should it be required to ship a battery pack, care must be taken when packing to ensure that it cannot be physically damaged.​

It has been reported that some Li-Po battery fires have been caused when a dog was attracted to the smell of a lithium battery – and bit it.​

Please contact the airline you are travelling with to get their policies and requirements BEFORE travelling.​

Consider a Lead-Acid (car) battery. The basic equation becomes:-​

Two dangerous materials are converted to two harmless materials during discharge!​

Unlike others, lithium-polymer batteries are reputedly ‘environmentally friendly’.​

It must be remembered that should the outer case of a Li-Po battery be compromised, the lithium inside is highly volatile and will react violently with water.​

For safety reasons, it is recommended that Li-Po cells be fully discharged before disposal.​

If the battery is physically damaged, discharge is NOT recommended. ​

Li-Po batteries must also be cool before proceeding with the disposal instructions.​

FOLLOW THE MANUFACTURERS DIRECTIONS FOR SAFE DISPOSAL.​

For Li-Po packs rated at 7.4V and 11.1V, connect a 150 ohm resistor with a power rating of 2 watts to the pack’s positive and negative terminals to safely discharge the battery pack.​

A suitably rated light bulb is a great load. Consider this:-​

A 100 Watt 12 Volt incandescent light bulb will draw 100/12 = 8.3 Amps.​

Although the light bulb may not light up, it is still connected to the battery, causing it to discharge. Even though the bulb is not shining – LEAVE IT CONNECTED to ensure the battery is truly fully discharged. (We leave it for a week).​

After that there should be ZERO voltage in the battery. Cut the plugs off, bare the wires, and twist them all together to ensure it stays discharged.​

At this time all the active lithium should have been converted to an inert substance, and can be safely disposed of.​

Take the discharged battery to a battery disposal centre for incineration. ​

Some manufacturers claim that a discharged battery may be disposed of in landfill! Please don’t!​

WARNING – Salt Water Bath for Discharge​

Originally one manufacturer proposed discharging the LiPo battery in salty water, HOWEVER part of that process required the battery pouch to be sliced open to expose the lithium to the salty water!​

Slicing the battery pouch open is dangerous and many accidents were recorded. Additionally, lithium on contact with moisture burns so fast as to approximate and explosion! Lithium and water – bad idea!​

Attempting to discharge a lithium battery in salt water is NOT recommended. Either discharge the battery using a suitable light bulb OR take it to an authorised disposal/recycling place.​

• Keep Li-Po Batteries in a Cool Environment​
  • Do not leave Li-Po batteries in direct sunlight. Elevated battery temperatures increase the likelihood of the battery chemicals reacting in a hazardous manner.​
• Do Not Overcharge Your Battery​
  • Excessive charging will cause the battery pack to heat up, expand, or explode.​
• Handle Li-Po batteries Carefully​
  • Try to prevent holes being punctured into the battery. The chemicals inside the battery may leak out. These chemicals may become volatile in contact with air.​
• Dispose of Unwanted LiPo Batteries Responsibly​
  • If the battery is undamaged and you feel safe in doing so, a light bulb may be used to discharge a battery.​
  • If the battery is physically damaged, or if you do not feel safe in discharging the battery, take it to an authorised disposal or battery recycling store for disposal by professionals.​
• Never Leave Li-Po Battery Unattended While Charging​
  • Ensure the correct charge settings for the battery are being used.​
  • The charging area should be away from any flammable material.​
  • If smoke appears, or there are signs of the battery expanding, or “puffing out”, disconnect the battery charger from the wall socket, eliminating any further flow of energy into the battery.​
• Use LiPo Specific Chargers Only​
  • EXTREMELY IMPORTANT. Using a NiCd or NiMh charger will create an unwanted reaction within the battery that may result in a fire. Remember to only use Li-Po specific battery chargers!​

• Never Leave Li-Po Batteries Plugged to an Electronic Speed Controller (ESC)​
  • Li-Po batteries are always ageing, even when they’re not connected. The chemicals inside the Li-Po battery are extremely volatile.​
• Never Arc the Positive and Negative Terminals​
  • A positive-negative short creates a continuous flow of uncontrolled energy through the battery, with nowhere for the energy to be released. ​
• Check the Battery After Each Run Period​
  • Check for signs of puffing, for severed or cut wires, for dents and/or damage, and the overall condition of the battery. If the battery is starting to puff out, swell, or looks like it has been punctured, do not continue to use it.​
  • Charging a damaged battery MUST NOT BE ATTEMPTED!​
• Chemical Reactions of Li-Po Battery Are Not Instantaneous​
  • Be careful if you see a battery starting to smoke without fire. Although it has not yet reached the reaction of a fire, it is highly likely that it will reach the stage of combustion, and burst into flames. Remember, if you see smoke, UNPLUG THE CHARGER FROM THE WALL SOCKET AND MOVE THE BATTERY TO A SAFE LOCATION. Wait at least 10-15minutes before moving it again just to be safe.​
• Never Leave Li-Po Batteries In Your Car​
  • This is for the same reason why you should store your Li-Po Batteries in a cool environment. Heat = Reaction. Reaction = Expansion. Expansion = Cause for burning! BE AWARE!​
• Do Not Leave Batteries Unattended With Children​
  • Children do not know how to handle a battery safely. Be extremely careful and limit access to batteries. There are no age restrictions with respect to the use of batteries, however common sense is required.​
• The ‘C’ rating – and it’s consequences​
  • A 3S 11.1 Li-Po battery with 5000mAh have 1C = 5 ampere. If the battery is rated for 25C continuous use that means it can output 125 ampere (almost 1400 watts).​