Batteries in airsoft - how to pick one and use it properly?

Batteries in airsoft - how to pick one and use it properly?
9 November 2020

Batteries are a very important part of the equipment when it comes to electro-pneumatic airsoft replicas (AEG, AEP). On the market we can find mainly 2 categories of batteries - Nickel based (NiMh most common) and Lithium based (most common LiPo, also common LiFePo, LiIo). What they have in common is that they rely on chemical reactions to store and release energy and that they consist of cells that are connected in parallel and / or in series to give us the necessary voltage and capacity.

 

Let's divide the most important characteristics of batteries conditionally into primary and secondary. Not because some are more important than others, but because most of them are written on the package and we mainly pay attention to them when choosing a battery.

 

Among the primary ones, the first thing we will find on the packaging of an Airsoft battery is the capacity in mAh (milliamperes) - this is the amount of energy that the battery is able to store ( capacity ) and subsequently discharge. How long an electric motor can run depends on the capacity. The second is the voltage denoted by V (volts). The voltage is what the speed at which this motor will revolve depends. Higher voltage = more revs. The third, "hidden" feature is the maximum current that a battery is capable of delivering at peak and prolonged loads. It is measured in amperes - A. The current directly corresponds to the energy needed for an electric motor to overcome a load, within its capabilities. Higher current = higher load. This characteristic is called "hidden" because lithium-based batteries must multiply the value indicated on the package by "C" by the capacity converted to ampere-hours to obtain the required value in amperes. Nickel metal hydride (NiMh) batteries do not have this designation, but we know that even with the best NiMh batteries, this value does not exceed 2C, while with lithium it varies from 15C to 45C. A higher C value usually means a better quality battery and therefore more expensive.

 

For those who are very far from electricity, I will try to draw a parallel with water - imagine that the battery is a water heater. The volume of the boiler is the capacity of the battery (Ah or mAh). The voltage (V) is the pressure in the pipes and the current (A) is the degree to which the drain cock is open.

 

Secondary characteristics are no less important, but in this article we will label them this way, because these are characteristics that we pay attention to later or that we do not know at all and do not bother to understand.

 

1. Energy density of the battery - this is the capacity that a battery can have in relation to its size. It is measured in watts per liter - Wh / L and varies with NiMh batteries from 140 to 300, and with LiPo batteries from 250 to 730. Very roughly speaking, in bodies with the same volume LiPo batteries will have about 2 times more large capacity NiMH with maximum voltage.

 

2. Charging efficiency or Coulombic Efficiency (CE) - this is roughly the charge that a battery can give compared to the charge it has taken. At 100% efficiency and charged 1000 mAh, the battery will give 1000 mAh. At 50% - when charged 1000 mAh, the battery will show complete exhaustion at 500 mAh. For NiMh batteries, this efficiency varies from 80% to 50% and decreases with each successive cycle of operation. In LiPo batteries it exceeds 95%, and in some 99%, and over time, with proper operation, it can grow and reach 99.9%, which makes these batteries extremely effective.

 

3. Self-discharge rate - this is the percentage of energy that the battery loses without being used for a certain period of time. It is customary to measure in percentage / month or percentage / year. It depends directly on the outside temperature, the battery charge from which the measurement starts and the condition of the cells. NiMh batteries can lose up to 35% of their charge in the first 24 hours, then lose up to 10% of their charge per month at room temperature (~ 20 C). At lower temperatures they can lose even more. On the other hand, LiPo batteries can lose less than 1% per year, at temperatures close to 0 C and provided that their initial charge is within 50-60%. Left to stay charged for a long time, LiPo batteries lose energy faster, but these losses are still well below the downtime of NiMh batteries.

 

4. Life - measured in cycles (charge-discharge). NiMh batteries have between several tens and 2000 life cycles, depending on the method of production, application, operation and storage. On average, the batteries we use in Airsoft have a lifespan of about 300-400 cycles. External mechanical influences have the strongest influence on these cycles (these batteries are strongly affected by shocks and even if they look intact on the outside, the cells inside can be damaged), affecting the way of charging and storage, and the way of operation. LiPo batteries, on the other hand have between a few hundred to a few thousand cycles. The exact duration depends on the same factors as NiMh batteries, with Lithium batteries being less sensitive to shocks. In both types, the battery capacity decreases with each subsequent cycle. Given the peculiarities of our hobby, both batteries are expected to live about 2-3 years with proper care.

 

These are just some of the important features of batteries, but this is time to ask an important question -why if an Airsoft replica is sold with a battery, it is not a LiPo battery, but an older NiMh battery? Is it just because of the price? The truth is that the difference in price is so low that for the end user NiMh battery would not be of much interest. The key is elsewhere - "self-ignition". This is the word that plays the biggest role in the emergence of this seemingly "phenomenon". There is no risk of spontaneous combustion with NiMh batteries, while with improper operation, storage and transportation LiPo batteries can ignite spontaneously. It is enough to damage the protective membrane of the LiPo battery, the chemical composition to come into contact with oxygen from the air to start a combustion process that is high in intensity and can not always be extinguished quickly and easily. A flammable lithium-polymer battery burns about 2,000 degrees Celsius, which is enough to ignite not only the cardboard package in which the replicas usually travel, but also the replica itself. It is important to know that the risk of self-ignition exists not only when the membrane of LiPo batteries is damaged, but also when they are overcharged and undercharged.

 

Airsoft communities often hear that NiMh batteries "carry" overcharging and discharging. This is not the case, these batteries would also be damaged, but when charged with a current lower than 0.1C (1/10 of the battery capacity), the modern NiMh battery can "absorb" excess energy for some time without strong overheating and without damage. Another important feature of NiMh batteries is the so-called "memory effect". It means that the batteries give only the charge they have taken, no matter what charge they had before. With an incomplete charge cycle - ie. if the battery is not completely used up, for example at 50% and is charged to 100%, it will give only those 50% with which it was recharged. This effect occurs gradually, ie. the first time it will give 90%, the next 80% and so on until it reaches the capacity with which it was last charged. This effect is reversed when fully charged and discharged.

 

For lithium-based batteries, it is important to balance the charge in the individual cells. In order to get the required voltage of LiPo battery for operation in an airsoft replica (7.4V, 11.1V, 14.8V), we need to connect 2, 3 or 4 cells with a nominal voltage of 3.7V in series. Due to a number of factors, these cells may not be charged / discharged in the same way during operation, which we can understand from their different voltages. The nominal voltage of a cell shows only what charge it would have in the most stable position, at about 50% charge. Fully charged, this cell would have a voltage of 4.2V, and fully discharged - 3.2V. A difference in cell voltage of more than 0.03V can lead to subsequent recharging or recharging of any of the cells and damage to the battery. It is best to monitor the voltage of the cells with a tester for LiPo / LiIo / LiFePo batteries, and to balance them with a quality charger.

In conclusion, let's summarize how is the best and correct way to use these 2 types of batteries.

 

NiMH:

- It is best to charge immediately before playing with your original charger or with a smart charger that can monitor the battery temperature and allows pulsed charging of the battery.

- Care must be taken not to damage the batteries - this shortens their life cycle and capacity.

- Charging should be done at room temperature and avoid charging at low (close to 0 degrees Celsius) or high (above 35 degrees Celsius) temperatures.

- Do not leave the battery on the charger for more than 4.5 hours - this may damage the battery.

- After a long time without use,, it is a good idea to run the battery for a full charge / discharge cycle before using it.

 

Use the battery in warm weather, as it discharges much faster in cold weather. If you observe poor performance in winter, do not rush to throw it away, it is possible that in summer temperatures it works quite satisfactorily.

 

LiPo:

- The first is the use of quality chargers and charging the batteries only under supervision and in a non-flammable container.

- Charging is best done with a current of no more than 1C x battery capacity. It is recommended to charge in stages - starting with current = 1C, as the current decreases with increasing charge, reaching 0.1C at the end of charging.

- It is highly recommended that the batteries be disconnected from the replicas after use (especially for replicas with electronics) and if they will stay long without use, they should be charged at 50-60%.

- It is recommended to use the battery with the largest capacity, which fits in the replica being used. This will not only ensure longer and short-term operation (it can be used for a whole gaming day, not part of it), but also in the long term - partial, instead of completely draining the battery increases its life.

- Monitoring cell balance is highly recommended.

 

 

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