First thing you need to understand is just what an AMP-HOUR is.
simple version is if a battery is rated for 1 AH (amp-hour) and its fully charged that you can draw 1 amp for one hour and the battery will be depleted.
The second thing is what's depleted,,, that is when the manufacture says the battery is dead. It's some loaded voltage, typically 11 volts.
Then there is the base line math.
1 AH means 1 amp load for 1 hour
it also means that a .5 amp load at 2 hours, or a 2 amp load to .5 hour.
So that is the really basic level explanation.
Now into the real world.
A 50AH battery will support a 10 amp load for 5 hours.
But we are talking about a radio that is not being talked on constantly.
The radio draws 1 amp when it's receiving, so if it never transmitted, it would run for 50 hours before the battery was flat.
But since you are talking on it, it will draw 10 amps when you are doing that. So the discharge rate is much higher when you are transmitting.
Figuring out exactly how long the battery will last is difficult, and in truth, can only be a good estimate as you cant tell how long you will be talking on the radio as opposed to how long you will be listening to it.
So saying a 50AH battery will last until 5PM tomorrow running radio X is near impossible to honestly state.
There are some ratios that get thrown around, but you are never going to accurately predict the point that a battery will go flat with a varying load. And if you add a charger to the mix, the current available from the charger gets into the math. If a 5 amp charger in running, you are putting 4 amps into the battery and one amp is going to the radio. But if the radio is transmitting, you are supplying 5 amps to the radio and the battery is supplying 5 amps and is discharging during transmit. Then it goes back to receive and we go back to the 1 and 4 amp feeds.
I am hoping that sort of helps. And it shows you that trying to make an accurate calculation is very difficult, and while you can get reasonably close it's still sort of a guessing game.