mA vs. mAh

Simple question I never bothered to ask,

mAh is the amount of time a source can discharge at a constant rate. I often see mA used to describe this rate. My question is, if a board is said to run at 15 mA, is this 15 mA per second, or is 15 mA some kind of instantaneous measurement?


Yes it is both an instant measurement and per second. Current is defined as the flow of charge per second, so it is like speed both an instantaneous and a sustained rate.

You have the definition of mAH wrong though, there is nothing constant about it, it is the current flow over time.

If a battery is 2000mAh, that is the total capacity of the battery. That means it can supply 2000mA for an hour or 2mA for 1000 hours (if the battery is an ideal perfect battery).

Can I take it one step further ? The meter for electricity in your house measures in kWh. That is the voltage times the current during a certain time. Instead of using the average per hour, often per month or per year is used. For example 100kWh per month.

Or put another way 1mAh = 3.6 coulombs of charge.

Note that battery (or cell) capacities are normally related to their c / 20 discharge rate. Thus, a 2000 mAh battery can be expected to provide 100mA for 20 hours, but cannot be expected to provide 2000mA for one hour.

And that's for an overcharged brand new cell at the optimum temperature, since manufacturers are interested in their products appearing as good as possible compared to the competition.

Expect a 2Ah cell to provide >= 1Ah throughout its life and you'll be less dissapointed than if expecting it to provide 2Ah throughout its life. No battery technology is anything like perfect.