There are 4 characteristics of batteries that we want to know:
- Voltage - measured in Volts (V)
- Amperage - measured in Amps (A) - also measured in units 1-thousandth (1/1000) smaller called a milli-amp. 2A = 2,000 milli-amps.
- "C" Rating - explained below.
- Type of battery (to come).
Here we with deal with the first 3 items - Volts, Amps and the very confusing "C". They can be thought of as water in a large water tank:
- Voltage is the temperature of the water - the hotter the water, the more work it can do.
- Amperage is the amount of water in the bucket - as you use the water, there is less and less of it left until you recharge your battery (of fill your tank). A smaller tank would have fewer Amps in it.
- The "C" rating - this is comparable with the size of the valve that's used to fill or empty the tank.
Let's say we have 2 different 10-gallon tanks. One of them has a garden hose connected to it, and the other one has a fire hose connected to it. The first one would have a low "C" rating because it would take a long time to empty it or to fill it.
The second tank (the one with the fire hose), would have a high "C" rating because it could be emptied (and filled up) much more quickly.
Having a low "C" rating is not a terrible thing - regular AA batteries have a low "C" rating but they last just fine in your TV remote. However, if you try to use them in a high-"C" application such as your digital camera you'll find that they get hot and run out very quickly. On the other hand, batteries with high "C" ratings are more expensive, which is why you don't want to use your expensive camera batteries in your tv remote.
Some numbers now:
- a 2,000 ma battery with 1 C rating, should not be charged or discharged at more than 2,000 ma per hour (2,000 ma/h).
Charging & discharging this battery will take 1 hour.
- a 2,000 ma / 10C battery, can be charge or discharged at 10x that rate 20,000 ma per hour (20,000 ma/h).
Charging & discharging this battery can be done in only 1/10 of an hour, or 6 minutes.
- a 2,000 ma / 20C battery, can be charge or discharged at 20x that rate 40,000 ma per hour (40,000 ma/h).
Charging & discharging this battery can be done in only 1/20 of an hour, or 3 minutes.
The higher the "C" rating, the quicker we can use up the battery's charge.
Know that we know what it is, what do we do with the information?
Well... for instance, if a battery is rated for 2,000 milliamps / and 10C, we never want to discharge it faster than 2,000*10= 20,000= 20A. If you use this battery with any motor/prop combo that uses more than 20A you will damage the battery right away.
The next thing to keep in mind, is that if you use something right at the top of it's limits, you will not get all the life of out it that you otherwise might. Using a 10C battery at 5C will make it last a whole lot longer than if you use it at 10C all the time. Be conservative here and you will save money and hassle in the long run.
Another thing to keep in mind, is that all batteries have two "C" ratings - one for charging and one for discharging. Most Lithium-Polymer (LiPo - pronounced Lie-po) batteries have 1C charge rate so they can be charged in 1 hour, regardless of how fast they can be discharged. Nickel-Metal-Hydride (NiMH) batteries can be both discharged at high "C" and also charged at high "C" rates.
Lastly, realize how un-friendly we are to our batteries. Your laptop uses Li-Po's and it can run about 3 hours with them. This is a 1/3 C rating, while for flying, we would not even consider anything below 10C which is over 30 times faster ! A 30C rating would be 90 times faster discharge than your laptop!!!
