Okay, so basically, to calculate the basic amount of time that you need to charge your battery for, you need to understand a few basic electrical and mathematical rules.
#1. Voltage is a measure of the energy carried by each electrical particle inside your circuit. This is measured in Volts.
#2. Current is how much particles are flowing, how fast. This is measure in Amperes, or Amps.
#3. All natural metals and materials, at room temperature, have electrical resistance. This means that they will naturally want to prevent electricity from travelling through them. Resistance is measured in Ohms.
Once you've understood those three points, you can look to your battery and wall charger. To charge your battery, you're mostly going to look at your charger's OUTPUT (Not INPUT) Amperage. Because most batteries are measured in the mA, or MilliAmperage range, the rating is going to look something like:
[Output: DC 8v 300mA]
This means that the charger outputs 300 MilliAmps of electricity at 8 Volts of energy, with a Direct Current. Be VERY certain that your charger does not say AC. This is Alternating Current, and cannot be used in any formal appliance or charge without a rectifier. If you have an AC OUTPUT CHARGER, you have a problem.
Now, look at your battery. Most stock batteries will look something like this:
[Ni-Mh 2/3A 8.4V 1100mAh]
Disregard the 2/3A and Voltage for now; They don't factor into your charging.
The Ni-Mh, Li-Po, or Ni-CAD on your battery tells you what type of battery you have. Most stock batteries are Ni-Mh, or Nickel Metal Hydrate batteries. These have the advantage of not needing discharge (Like Ni-CADs), and not exploding if handled improperly (Like Li-Pos) although you still should exercise caution around them.
Now, look at your mAh rating. mAh stands for MilliAmperage Hours, which is basically a rating of how many Amperes (or MilliAmperes) your battery will transmit in one hour. Most stock batteries range from the 1000-1500 range for a mini-type battery and 1500-2000 range for a large-type battery, although I have seen the occasional 300 and 3000 mAh ones.
Basically, after that long rant, you now have two important pieces of information.
#1. Your Wall charger's output power, in mA.
#2. Your Battery's Charge rating, in mAh.
Because the two units are the same, you simply divide the battery's rating by the charger's rating. For the above example, that would be
1100 / 300 = 3.66...7
So, you would charge your battery for 3 hours and 40 minutes.
So, now you've successfully charged your battery! Your brain is probably exhausted after all that comprehension, so here's an alternative.
Get a Smart Charger.
It does all that work for you, so you don't have to.
Hope that helped! Enjoy!
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Last edited by JLiang; March 21st, 2012 at 20:17..