Yes, it is the current drawn divided into the mAh, to determine battery duration, in hours. But it is always confirmed experimentally, and normally separately. One for constant talk time, and one for constant standby time. The combined, if even given, is an agreed upon combination of the two. Clearly it varies with the actual use. Also, it varies with how strong the radio signal is to the phone. I think that a very good signal is assumed to give the 'best' numbers. Each phone consumes different amounts of battery power. If you can actually change the battery to a larger one, it would be linear, for the most part, that is a 1000mAh battery should give 2x the talk/standby time as a 500mAh one. Hope that this is clear.