In another question, I was trying to figure out what kind of battery I could use to provide enough current to power my circuit. Someone pointed out that batteries often have a maximum discharge rate. In looking at data sheets, I found that these rates are often noted in units of "C."
At first I assumed it was related to coulombs and 1C was 1 amp for 1 second, but that doesn't appear to be the case (except, I guess, coincidentally for a 60,000 mAh battery maybe?).
Instead it appears that 1C is the nominal rating of the battery? So, a battery rated at 3500 mAh was tested and from fully charged it will discharge 3.5 amps continuously for 1 hour before it is fully discharged?
So, if I have a circuit that requires .5 amps and a 840 mAh battery, I only need a 1C maximum discharge rating to be able to power my circuit? Will it power my circuit for roughly 1.68 hours (potentially more because of the reduced stress)?
If, on the other hand, I switch to a battery that's rated at 2700 mAh, then my current draw is closer to .2C or .54A/hour? Would that power my .5A circuit for roughly 5 and a half hours?
Finally, why do we rate batteries this way? And why isn't the maximum discharge current rated in amps instead of ratios of discharge rates?