The letters “mAh” stand for milliampere hours – it is how a battery’s energy storage capacity is measured. This also tells us how many electrical currents are released in an hour.
m = milli = 1/1000
A = ampere, a unit of electrical current (usually shortened to “amp”)
h = hour
Therefore mAh means 1/1000 of an ampere for an hour. It is equal to 3.6 coulombs.
For example, if you have a rechargeable battery with a capacity of 2700 mAh (or 2.7 AH), and it is used to power a device that draws 1 ampere of current, therefore if that battery is fully-charged then it can power the device for 2.7 hours.
The higher the mAh rating then the higher the energy capacity of a battery and longer the battery cycle. Typical rechargeable batteries are rated between 1800mAh and 2700 mAh, it can also be purchased in different sizes (AA, AAA, 9V, etc). We can now determine how long your battery will last by mAh. Under normal usage it is 45 minutes for every 100 mAh (approximately).
Digital cameras, PDAs, digital video and hand-held video game systems are usually high-drain devices. And all of those devices will perform well with rechargeable batteries which have a higher mAh.
Difference between voltage and amperage.
Voltage is how much electricity there is, whereas amperage is how fast that electricity if moving.
As an analogy, imagine that we are driving to the cinema in our cars. The “voltage” here is the desire we have to get to that cinema, while the “amperage” is the speed with which we are getting there.