Over the last few weeks I noticed a lot of repeat battery questions. So, I dusted off a battery guide I found on the web, rewrote parts, added parts, and rearranged parts to make it easier to get to the main info. I don't remember where I got this guide exactly so if it is yours in part speak up and I will gladly share the credit for its creation.

Also, if you see any problems with the guide please feel free to add to the information.

It is rather long but the first section or two is the stuff that most people want to know.

Battery Basics

Tech Terms

mAh: MilliAmp Hours. A 1 mAh battery could last ~1 hour at one milliAmp load.
Amps: Amperes, Current
Volts: Voltage
Ohms: Resistance
NiCd: Nickel Cadmium. A rechargeable battery chemistry.
NiMH: Nickel Metal-Hydride. A rechargeable battery chemistry.
LiPoly: Lithium-polymer rechargeable chemistry (expensive)


Rechargeable Batteries

There are 3 principle chemistries of rechargeable batteries recommended for AEGs: NiCd, NiMH, and LiPoly.

LiPoly batteries are recently coming into usage for airsoft -- while voltage options remain limited (the most common is 11.1 volt), they are about the right size for airsoft, and if you take care to not heat up the gel-packs, are an extremely good high-ROF battery. This battery is recommended for upgraded AEGs only.

NiCd batteries are probably the most common type found in airsoft AEGs. They come in two basic cell sizes, AA (mini cell size) and sub-C (large cell size) and each cell produces 1.2 volts of power. The capacity of the cells vary from ~500 mAh to ~1800 mAh. By stringing together NiCd cells you determine the final voltage of the battery pack. 7 cells = 8.4 volts, 8 cells = 9.6 volts, 9 cells = 10.8 volts, and 10 cells = 12 volts. However, a battery pack’s capacity is determined by the mAh of one cell. Each cell is discharging it’s mAh at the same time.

Example: An 8.4 volt, 1000 mAh NiCd battery can produce 7000 mAh of constant current for ~one hour through a 8.4 volt electrical “faucet”. 7 cells x 1000 mAh = 7000 mAh total current.

Two more things concerning NiCd batteries: First is the need to discharge the battery before you recharge it. If you don’t, the battery “remembers” and resists taking on a full charge. (I have read a few commentaries that suggest discharging is not necessary but conventional wisdom says to discharge) Secondly, after recharging, the battery will lose about 1% of its charge per day just sitting on the shelf.

NiMH batteries are also, very common in airsoft AEGs. They are a bit more expensive, but they have a higher capacity (up to 3300 mAh). NiMH are a bit more difficult to charge than NiCd, so make sure your charger is able to handle them. NiMH batteries also have a higher rate of self-discharge, losing about 2-3% a day. Discharging the NiMH before recharging is not necessary.

Charging Batteries

One of the most important things about charging up a battery is not to over heat it. The battery should never get so hot you cannot pick it up easily with your bare hand. Once the battery begins to get a little warm you need to stop charging.

In order to estimate how much charge you have left in your battery without a voltmeter you can expect to use 1 mA per shot in most stock AEGs. If your battery holds 1000 mAh then you should get ~1000 shots before the battery loses power. This is especially important for NiHM batteries because you do not have to discharge them before recharging. If you estimate that you shot 500 bbs in the last skirmish you probably have half a battery full. Use this information to help determine charging time for NiHM batteries.

There are several types of chargers available. If your charger does not shut off automatically there is a simple way to estimate the recharge time. Almost every charger I have seen has its mA output written on the charger. So, if your battery has a 1000 mAh capacity you divide that by the mA output of the charger to get the number of hours to charge the battery.

Example: 1000 mAh (battery capacity) divided by 500 mA (charger output) = 2 hours (some say to add 10 to 20% to the answer)

Trickle chargers, which plug into the wall, and then into the battery, charge the battery at a very slow rate (typically between 200 and 500 mA, so charging usually takes several hours). They look like a regular wall mounted transformer (or a "wall-wort") with a wire plug that connects to the battery. There are different kinds, be sure the charger voltage matches the voltage of the battery. They can and do overcharge the battery if you leave them plugged in too long.

Timer -based "fast charger" (I have been advised against fast chargers because they can send too much current into the battery too fast if not set correctly. You should not charge a battery faster than its capacity. For a 1000 mAh battery the charger should not charge at a rate greater than 1000 mA.) - These chargers can charge up a battery in an hour or so. They typically feed it with a few amps of charging current. Most of these units (around $20-$30) are a small box with a few switches/dials for setting the battery voltage and/or the charge time or battery capacity. There is one wire that goes to a wall plug, and another that goes to the battery. They charge at a fast rate, and use a timer (that you either manually set for a certain amount of time, or calculated based upon the capacity that you told it your battery had). The problem with this is that the charger has no idea when your battery is really full. These can undercharge the battery (resulting in less battery time for your AEG, and possible memory effect if your battery capacity is more than the charger was set for. If there is still some power left in your battery, the charger will most likely overcharge it, which can cause it serious damage. It is important that you use a battery discharger to make sure that the battery is empty before you charge it back up if you are using one of these chargers.

Peak Chargers (also called an "intelligent charger" or a "smart charger") can be acquired as well. This is the best type of charger you can have. These chargers can detect the slight drop in voltage that signals that the battery is full and automatically switch themselves off. These chargers also usually incorporate a discharger as well. These chargers typically cost $40 and up, and look similar to the timer based chargers, except that they are usually bigger and have more switches/dials/indicators on them. One very popular charger in the world of airsoft is the $50 TLP Intellicharger, that can run off 110 volt AC, 220 volt AC, and 12 volts DC. A peak detecting charger can help you ensure that your batteries are in tip-top condition and they charge batteries quickly. You can save a little bit of money by getting a cheap timer-based charger, but your batteries will thank you if you buy Peak instead. Before charging any NiMH batteries on your Peak Charger, ensure that it is designed for that or you may risk damaging the battery.


The following information is for those who want to understand the battery issue in more detail. Enjoy.

Batteries, Airsoft and You

Batteries for airsoft have two general characteristics, voltage and capacity. Capacity is measured in mAh. Voltage is measured in volts. Amps are a measure of how strong a current is. Capacity is just how much power the battery can hold; it is basically how long you can use the battery before it stops being able to power the system. Amps measures how much power a battery can push out. Voltage is how fast it pushes.

Think of a battery as a water balloon. The mAh measures how much water is in the balloon. Voltage tells you how big a hole you have in the neck of the balloon. Amps tell you how much pressure is being exerted on the balloon. Resistance measures how much fabric you have blocking the water from coming out.

So...more or less mAh is more or less Water. Basically what volume of water you have to work with. Voltage tells you how much water you can let out of the balloon at one time. A bigger neck on a balloon will let more water out at one instant. More or less amps measures how fast the water is moving out of the balloon. More pressure on the balloon makes the water come out faster. The Resistance over the neck slows the water from flowing. The less resistance, the more efficiently the water will be delivered.

The main things Airsofters are concerned with are how much water they have and how much they can deliver at one time. mAh and Volts. For advanced users, the discharge rate (measure in Amperes, varies from 20A to 35A -- 30A is ideal)

You should usually aim to get the battery with the highest mAh rating you can because it will last longer. This is why it is preferable to use a "large" type battery (generally between 1200mAH and 3000mAH) as opposed to a "small" type battery (generally 600 mAh). There will be no adverse side effects to using a battery with a higher capacity; it will simply last longer before it runs out of juice. A battery with a higher mAH rating will not damage a gun.

The capacity rating of milliAmp hours means that if you drew the rated amount of milliamps from the battery, that the battery will last for 1 hour before "dieing". For example, a 3000 mAH battery can deliver 3 amps (1 Amp = 1000 milliamps) for one hour continuously, 6 amps for 30 minutes, or 1.5 amps for 2 hours. A battery's rating is usually "\20H", meaning that the rating is for 20 hours. For example, a 3000 mAH battery is specified to deliver 150 mA for 20 hours. The batteries will have a slightly less capacity in an AEG application (where they will be providing a high current for a short time) since the higher load is more stressful for the batteries, but you can still compare mAH ratings between batteries.

The battery's voltage determines how much power the motor will have. Stock AEGs take an 8.4 volt battery. Upgraded AEGs sometimes need higher voltage battery packs, such as 9.6, 10.8, and the insane 12 volt pack. The higher voltage will make the motor turn faster (higher ROF) and/or harder (to drive those bigger springs). Please also note that a higher voltage battery will put much more stress on your motor and the mechbox internals. You can easily tell what voltage a battery has by counting the number of cells; each NiCd or NiMH cell is nominally 1.2 volts. A 10 cell pack has 12 volts. A 7 cell pack is a standard 8.4 volt pack. The power of the motor (measured in either watts(W) or Horsepower(HP), 746 W = 1 HP) is a function of the voltage it is being fed and the Current it is drawing. Watts equals Current (in Amps, 1000 Milliamps = 1 Amp) times voltage. Please note that the motor will draw more amps running at a higher voltage since it acts somewhat (not quite, but good enough for a simple comparison) like a resistor. The motor follows Ohm's law: Current(in amps) = Voltage divided by Resistance (in ohms). The resistance of the motor stays somewhat constant. So, the amount of current the motor draws will increase linearly with the voltage. Since the power of the motor is volts multiplied by current (which also increases with the voltage), the motor's power increases with the square of the voltage, while the current increases linearly with the voltage increase.

Resistance

Each cell of a battery has internal resistance, which limits the power it can put out. A cell with the lower Internal Resistance (IR) will always be better. Early NiMh cells had a high IR making them not perform as well as NiCd or recent NiMh cells. Also, the connectors, wire, and battery bars in a pack all have resistance. Resistance is what is stopping the flow of electrons. The lower resistance in everything, the better. The stock connectors on pack are horrible. They have high resistance, and over time will wear out and get even worse. Getting some low loss connectors such as Deans Power Plugs will help to cut down on the resistance. The wire is also a place where you can cut down on the resistance. You can use some 12 gage wire in place of the thin wire that some pack have. Also, if you look at regular battery pack the cells are connected with thin, foil like strips of tin. These are horrible compared to solid copper, or silver and gold plated battery bars you can get. Each of these things alone may not seem like a big deal, but by replacing the connectors, wire, and battery bars you can reduce the resistance in the circuit.

Getting more technical

Let's assume that we have a motor, running at 8.4 volts, and drawing 10 amps (a guestimate...nice round numbers). This motor puts out 84 watts of power, and has a resistance of about 0.84 Ohms. Now, if we were to increase the voltage of the battery pack to 9.6 volts, the motor will draw about 11.43 Amps, and will put out about 110 watts of power. A 10.8 volt battery pack will cause the motor to draw 12.9 amps and produce 138.86 watts of power. The somewhat insane 12 volt battery will cause the motor to draw 14.29 amps, and produce 171.43 watts of power (that's about twice the power! but we are only using 43% more voltage. Remember, double the voltage, quadruple the power, increase the voltage by the square root of 2, and you double the power). Note from this that the motor will drain the battery faster if a higher voltage battery pack is used, since it will draw more amps. For this reason, an 8.4 volt, 1500 Mah battery will last much longer than a 12 volt, 1500 mAh battery pack.

As shown by Ohm's law, an increase of resistance in the circuit will cause the current drawn (and subsequently, the power) to decrease. Therefore, it is extremely important to have the lowest possible resistance. For example, let's take the 8.4 volt, 0.84 ohm AEG from the voltage discussion that produced 84 watts of power. If we added an extra 0.1 ohms to the circuit (let's say it came from the battery connectors or something), the total resistance will increase to 0.94 ohms, causing the motor to draw 8.94 amps instead of 10, and put out about 75 watts of power instead of 84 watts. resistance can come from many different sources. One place where resistance can come from is the battery pack connectors. If you are fabricating your own battery pack, try to get the best possible connector for it. Another source of resistance are the various interconnects and wires in the gun and in the battery pack. If you are making your own battery pack, you should try to use the best bus bars you can to connect the batteries together. If you are rewiring your AEG, try to use the biggest (smallest gage number) copper wire that will fit in there. Resistance can also come from the AEG's fuse, this is one reason that people remove it. I do not like the idea of removing the fuse, since it is an extra safety measure incase of a shorted motor, etc. People also remove the fuse to make room for a bigger battery pack, or if the fuse blows frequently due to a higher current draw from the motor (rather than try to put in a slightly higher-rated fuse). Resistance can also come from the switch (in the mechbox, as part of the trigger/selector switch assembly). Higher currents and voltages can also cause the switch to wear down. I recommend using some contact cleaner and switch lubricant on it if you ever have the mechbox open (and put some of that contact cleaner on the battery connectors, too). The final source of resistance come from the batteries themselves. All batteries have a certain "internal Resistance" (IR). The better cells have a lower IR than the cheaper ones. Cells intended for (serious) R/C car duty are the best for airsoft, since they are engineered to have the lowest IR possible, so that they can deliver high currents for short times (as opposed to the higher IR, larger capacity batteries that would be preferable in less current intensive applications). The best cells are those made by Sanyo and Panasonic, though a number of 'GP' cells have shown to have very good discharge rates.


Executive summary


* mAh and Volts are what is important: how much juice you've got and how much it puts out
* Peak Chargers are best for conditioning your batteries
* NiCD Inexpensive and generally lower MAH, NiMH: Expensive but excellent performance
* While people 'know' there is some sort of 'memory effect' no one can explain how it works

This post has been edited by Bullfrog: Nov 22 2006, 01:14 PM