mAh stands for Milliamp Hour, a technical term for how much power a particular battery will hold. Digital camera batteries with higher mAh values theoretically last longer without requiring a recharge, allowing you to take more photographs before you have to replace your batteries.

It is recommended when placing batteries in a digital camera that their mAh values match. Otherwise, it is possible that one lesser mAh battery will drain before the others, causing extra strain on the remaining batteries or causing your digital camera to not work until all batteries are replaced.

‘mA’ per ‘hour’ - so 500maH would last 1 hour at 500mA or 2 hours at 250mA or 500 hours at 1mA.

Is this an indication of the level of mathematics training nowadays? Hmmm. Its always instructional to look at the units to see clues to how to calculate the value. For example, torque may be specified in N-m (Newton Metres), which says plainly that the value is calculated by multiplying the force in Newtons exerted at a distance from the rotational center in metres. Another example is in velocity in Metres/second. This tells you that to determine velocity you would take the number of metres travelled and divide by the number of seconds required to travel that distance. One more example is your value in mAH. You should know first that this is pronounced “milliamp hours” which tells you that it is the multiplication of the milliamps times the hours. So, if you have a battery that is rated at 800 mAH then theoretically they mean that you should be able to pull, say, 200 mA for a total of 4 hours from a fully charged battery before the battery is exhausted.

As Nigel mentions, these ratings are oversimplified in a few ways that you should be aware of if you want to be an expert on the subject. For example, the capacity of a battery in mAH is usually stated for a given discharge rate. This means that they measured the capacity by drawing current from the battery at a constant rate. The use the letter C to help specifiy this. For example, the capacity might be specified at a discharge rate of 0.5C. C means the rated capacity value (in our example above this was 800) only they mean just in mA, so a discharge rate of 0.5C means 400 mA for this particular battery. The other critical thing you should understand is that they choose the point where the battery is exhausted by seeing where the voltage drops to a point where it is becoming useless. Each type of battery, whether it is Alkaline, or Carbon, or Nickel Metal Hydride, or Lead Acid, or Lithium or whatever, has a unique curve of voltage vs time that you have to study to see the differences. One thing is common amongst them though, and that is that voltage decreases as the battery discharges, the voltage is not exactly constant.