By Tom ‘Anvil’ Hibberd
The most common type of Airsoft RIF is the AEG (Automatic Electric Gun) however these can be powered by a bewildering array of batteries!
What is a battery?
Batteries convert stored chemical energy directly to electrical energy. A battery or battery pack is a collection of individual cells or cell assemblies, with casings, connections, and in some cases electronics for control and protection. A cell is the basic unit that consists of electrodes, separator, and electrolyte in a container. For instance a 7.4V LiPo battery has two cells each of a nominal 3.7V
There are two types of battery, Secondary and Primary Cells. A primary battery is one that can not be recharged. A secondary battery is one that is rechargeable. Virtually all batteries used to power AEGs are rechargeable.
The rechargeable batteries that we use to power our AEGs must be charged before use; they are charged by applying electric current, which reverses the chemical reactions that occur during use.
- Type of Battery – LiPo (Lithium Polymer) Rechargeable
- Capacity of the battery – 1100 mAh (milliamp-hour)
- The nominal Voltage of the battery – 7.4V
- Max/Min Voltage of the cells – 4.2V/3.7V
- Max Charge Rate (per cell) – 1.1A
- C-Rate – 20C/30C – How fast the battery can safely discharge it’s energy, 60 mins / 20 = 3 minutes. Most batteries have two ‘C’ rating burst and continuous.
- The total battery power available 14Wh
We’ll now go through and explain what all of this means
TYPE OF BATTERY
There are several different types of Battery used in Airsoft AEGs, we’ll go over them here. In general our technology lags behind that used in RC vehicles and Drones. Pay attention to the instructions that come with your AEG. Most manufacturers are quite specific about the type of battery that you should use with your gun and ignoring this will void your warranty!
Pay attention to the instructions that come with your AEG. Most manufacturers are quite specific about the type of battery that you should use with your gun and ignoring this will void your warranty!
Back in the mists in time when I started the most common type was the Ni-Cad. This type of battery dates back to 1899! Compared to more modern batteries Ni-Cad has relatively low energy density and can suffer from reduced capacity unless fully discharged between charges. They are also quite bulky and took up a lot of space. A NiCad battery has voltage per cell during use of around 1.2 volts which stays pretty much constant until near depletion. The most common battery packs had a voltage of 8.4V (7 Cells) and 9.6V (8 Cells). For some of the smaller 600 mAh packs that could fit into awkward spaces you would have to change batteries every couple of hi-cap mags! Many players used fixed stock AEGs to house the large NiCad battery packs or even slings with built in pouches with battery wires running into the gun… Thankfully we have moved on!
NiMH (nickel metal hydride)
Alongside and eventually replacing NiCads are NiMH batteries, these can have up to two to three times the capacity of an equivalent size NiCd. Generally it is advisable to charge NiMH cells with a smart battery charger to avoid overcharging, which can damage cells. They have the same nominal voltage as NiCads and are produced in the same size packs (though with more capacity).
The voltage of a NiMH battery pack drops during discharge and this manifests as a noticeable drop in rate of fire. Although more energy dense than NiCads NiMHs are still relatively large compared to more modern designs. They don’t suffer from the memory problems that occur from charging a partially full NiCad and discharge in storage at a lower rate. They are considered relatively safe (more on that later) compared to LiPo batteries so many players continue to use them.
LiPo (lithium polymer)
A LiPo is a form of Li-Ion (Lithium-ion) battery, it is perhaps the most common battery used in airsoft today. the LiPo differs in a couple of ways from the batteries we have previously discussed. Instead of containing liquid chemicals LiPos have a semi-solid gel inside them. They have a high energy density and hence have a higher capacity for a given size than NiCads or NiMhs. The voltage of a LiPo cell depends on its state of charge and varies from about 2.7 (discharged) to about 4.2 V (fully charged). A fully charged LiPo battery of nominal 7.4V will actually have a Voltage of around 8.4V.
Unlike normal batteries which have a rigid metal case, LiPo cells have a flexible pouch. This is an advantage when weight matters for example radio controlled aircraft. This does mean that they are easily damaged if care is not taken. This can lead to catastrophic failure and fires in the worst cases. If a LiPo begins to swell it should be disconnected if safe to do so and taken to a safe place. Modern high quality LiPos have features designed to mitigate this to some extent.
LiPos have a high discharge current and better energy capacity compared to traditional batteries. This leads to a very noticeable higher rate of fire. The high discharge currents can damage the trigger contacts, so most manufacturers advise to either use a MOSFET or inspect the trigger contacts regularly.
For LiPo battery packs a specialised charger must be used to monitor the charge in the battery’s individual cells so that they are all brought to the same state of charge.
LiFe (lithium iron phosphate)
These are a form of LiPo battery but using different materials internally for it’s chemistry. They have a nominal voltage per cell lower than LiPo’s of around 3.2V but unlike LiPos maintain this voltage for most of the discharge cycle. They are considered to have better safety than a LiPo pack.
There are some new types of Li-Ion batteries (most notably from TITAN power), they can have a higher energy density than LiPos and hence a higher capacity. They use liquid chemicals and a rigid case rather than the gel and pouch used for LiPos. They have the same nominal 3.7V per cell and also need a specialist charger. One of the downsides of using a Li-Ion is that they degrade faster with charging than most LiPos dropping to around 80% capacity after around 300 charging cycles. The reality is however that most of us won’t ever be charging a battery for playing airsoft that many times so it shouldn’t be a problem unless you play every day!
CAPACITY OF THE BATTERY
A battery’s capacity is the amount of electric charge it can deliver at the rated voltage. The greater the size of the cell the greater its capacity. Therefore a small cell has less capacity than a larger cell with the same chemistry, although they develop the same voltage. Capacity is measured in units such as amp-hour (Ah), although in airsoft we normally use milliamp-hour (mAh) where 1 mAh is 1,000th of a Ah. High-drain loads such as AEGs can reduce total capacity.
The electrical driving force across the terminals of a cell is known as the voltage and is measured in volts (V). The voltage that is developed by energy release of the chemical reactions of a battery can generate different levels of driving force as we have seen above.
C-rating measures how fast a battery can discharge its energy. The higher the C rating the faster the power can leave the battery to turn your motor. It represents the number of times the battery could (theoretically) be discharged in an hour without being damaged or overheating.
For example a 20C battery can safely discharge in 5 minutes (60min / 20C = 5min)
Batteries have two C ratings, Constant and Burst. Constant represents the discharge rate in a device such as a torch or an RC Car. Most Airsoft guns are used to fire less than 30 seconds at a time so we should be looking at the C rating for Burst. It takes more power to start a motor turning than it does to keep it spinning. For an AEG or DMR with a stiff spring and a high performance motor this can mean loads of over 100 Amps for very short periods. This places a lot of stress on the electrical system and battery. High performance Airsoft guns need a high performance battery. Conversely a high performance battery can damage an Airsoft gun that isn’t set up for it.
“High performance Airsoft guns need a high performance battery. Conversely a high performance battery can damage an Airsoft gun that isn’t set up for it.”
To calculate how many amps a battery can constantly discharge you use the capacity of the battery (like 1500mAh) and the C rating of the battery (like 20C). Remember that a 1500mAh battery is actually a 1.5Ah battery. If you take 1.5Ah and multiply it by it’s C rating (in this case 20C) you get 30A, or 30 amps. So this battery can discharge 30A for 6 minutes until it’s totally empty without overheating.
A 1300mAh 20C LiPo can push 26 amps and has 1300mAh capacity
A 2600mAh 10C LiPo can push 26 amps and has 2600mAh capacity
Battery Power is defined by the equation
W = V * A
Thus, a battery pack that can deliver 1100mAh, that is 1.1Ah, while sustaining voltage of 7.4V (this happens to be in my LCT AK right now), can in theory deliver up to 1.1 * 7.4 = 8.1 Wh. We don’t tend to pay much attention to this in Airsoft but its a good indication of the overall energy potential of a battery.
TERMINOLOGY – Battery Technical Specifications
- Nominal Voltage (V) – The reference voltage of the battery, this normally what is printed on it.
- Charge Voltage – The voltage that the battery is charged to when charged to full capacity. This can be above the nominal voltage.
- Cut-off Voltage – The minimum allowable voltage. It is this voltage that generally defines the “empty” state of the battery. Going below this can damage the battery.
- Capacity (Ah for a specific C-rate) – the total Amp-hours available when the battery is discharged at a certain discharge current (specified as a C-rate) from 100 percent charge to the cut-off voltage. Capacity is calculated by multiplying the discharge current (in Amps) by the discharge time (in hours) and decreases with increasing C-rate.
- Cycle Life – The number of discharge-charge cycles the battery can experience before it fails to meet performance criteria.
- Maximum Constant Discharge Current – The maximum current at which the battery can be safely discharged continuously.
- Burst Current –The maximum current at which the battery can be discharged for bursts of up to 30 seconds
Batteries are available in a huge variety of shapes in order to fit into the tight confines of an Airsoft gun. Before LiPos became popular the shapes were more limited due to the rigid cylindrical cells that needed to be used. With the pouch type Lipo batteries it’s become easier to find a shape that will fit your AEG.
Named after the weapon these batteries use two or three banks of cells connected by wires. They are most commonly used in the stocks of AR type AEGs. A variant of this type is the Butterfly battery that uses flatter cells but the same construction to fit under the hand guards of some Airsoft guns.
Usually long and relatively slim these batteries are often found under the top cover of AK AEGs. Some really thin packs can fit inside the mock gas tubes and freeing up lots of space for other components such as MOSFETS. Mini sticks are a shorter type that can be used inside the stock tube of an AR or even inside the buffer pad on the end of a stock. They can be a gods-end for people attempting to replicate a particular real-steel gun.
Neither long and slim nor flat these are slabs of batteries. They used to be very common but are now mainly used in dummy PEQ boxes and inside fixed stock AEGS
Ultimately you need to connect your battery to your gun! There are a couple of connectors used to do this, the two most common are mini-Tamiya and Deans. You may also find a small white connector on a separate set of thing wires, this is a balance connector and its purpose is to allow a charger to individually charge each cell.
A Mini-Tamiya connector as its name suggests is a smaller version of the Tamiya connector, which is commonly used on low end radio-controlled models. When Tokyo Mauri created the AEG as we know it in the early 1990s they were also making RC kits so they simply brought over the technology they were already using. It is still probably the most commonly used connector for airsoft batteries. The built in lock makes it harder for them to come undone under vibration. They were designed for relatively low currents and modern high performance batteries and guns can over-reach these specifications.
These are a newer type of that has a tighter connection and less resistance than Mini-Tamiya. This leads to a small increase in performance and can also mean less heat generated in operation. Deans connectors require a soldering unlike Mini-Tamiya so changing over is recommended for experienced gun-techs only. Deans connectors can handle higher currents and loads so are recommended for high performance builds. The major downside to Deans is that most AEGs and batteries are wired for Mini-Tamiya and if you need to swap guns or borrow a battery then you may be out of luck. One solution is to always have a convertor (one end Mini-Tamiya, one end Deans) in your game bag. This will remove the advantages of Deans but may keep you playing!
There are other connectors that have been developed for RC sports, these offer advantages to Deans and especially Mini-Tamiya but are rare in Airsoft so will exacerbate any difficulties in compatibility.
CHARGING AND CHARGERS
Perhaps the most important aspect when talking about batteries is how to charge them. Some beginner packs come with a very basic wall trickle charger. These are best never used, they generally don’t shut off when the battery is full and continue to charge it. There have been numerous house fires resulting from the use of these chargers and especially in the case of batteries without on board protection electronics can be very dangerous.
Here at Airsoft Action we recommend that everyone use a smart charger that is appropriate for the battery type that they are charging. Be careful when purchasing a charger, there are lots of fakes and copies on sale especially on Auction sites. We suggest that you get yours from a reputable retailer that offers a proper warranty.
You should also always be present at watchful when batteries are being charged and in the case of Lithium batteries (LiPo and Li-Ion) it is also recommend that you charge them inside a fire proof battery bag.
Most smart chargers will require you to connect both the main battery lead and the balance connector. You should NEVER charge a LiPo, LiFe or Li-Ion battery on a trickle charger or non-smart charger.
TRANSPORTING AND STORING BATTERIES
It is tempting to just throw batteries in your game bag but as outlined above this can lead to damage and failure. I’ve personally seen batteries catch fire inside gun cases after rough transport. Always transport batteries inside a rigid box or container that protects the pack from damage.
It is also best not to transport batteries inside of the AEG itself and not to leave them inside the gun after use. This is especially true for RIFs with MOSFETs where the (slight) drain from powering up the device can deplete the battery past its cut off voltage causing damage.
Whilst at home keep your batteries in a safe place, away from sunlight and sources of heat. When storing a battery for a length of time it is recommended that you use a storage charge to best preserve it life. Good smart chargers will be able to do this for you and this is another good reason to have one!
Though we have covered a lot of ground in this edition of Airsoft 101: It really boils down to a few things. Following the manufacturers recommendations for which battery you use. Use a smart charger from a reputable supplier and always watch while charging. Transport and store your batteries in a rigid safe container and make sure they are in good condition. That way you should be fine!