Simple..

At the fundamental level, wouldn't it be coulombs that decreased?

Best way to find info is to look on the batter manufacturers website.
It also depends what type of cell you are talking about.
A typical dry battery, say an Alkaline AA will give 1.5v when new, to get usefull life out of it you will need to run it right down to about 1v.
As the voltage reduces the current drive capability will also reduce.
In a 6v batter pack made up of 4 C cells we would see faulty ceels down at about 1v while the other 3 in the pack were still at say 1.4v. The low voltage cell would also have severely reduced current output.

It also depends how much current you are drawing, if you are drawing a few milliamps a battery a 1v will have no trouble, however if you are drawing say 0.3A a low voltage cell may be ok for a second or two, but it will then loose current and voltage, it will recoverwhen off load again.
Del

"In case of cells.. We normaly says that "charge went out".

I've never said that in my life. So, you cannot say that people, "normaly" says that charge went out, unless you include some geographic, cultural or social frame of reference to indicate the particular geographic, cultural or social environment from which you speak.

Now, go back and start over!

Bit pompous don't you think. You knew what he meant I assume?

Nope.

Certainly it is a drop in voltage. Considering the constant load, As long as the battery can maintain the rated voltage,it would deliver rated power. A drop in voltage is the cause for drop in current.

Voltage is one thing, and amperage is another. a battery fails when it no longer supplies sufficient volt/amps (watts) to drive a given load.It's called Ohm's Law.

http://www.the12volt.com/ohm/ohmslaw.asp is a link that should explain it for you

As some have alluded to "charge went out" or similar expressions literally mean that the charge goes out. Putting it another way, " electrons move away or out of one place to another".

For a capacitor this is simply electrons crammed in one "place", so creating a high potential, moving to another where they are not so crammed and so being at a lower potential.

In this case the the voltage of the source point goes down in proportion to the fraction of charge, or original number of electrons, that is/are moved.

The above translates to a battery, except that in this case the electrons are stored in a chemical form - a chemical "place" if you like. The electro chemical bonding in different chemicals or materials are different and if any two (suitable) materials are connected together then electrons will tend to flow from the material with the higher potential to that with the lower potential (galvanic corrosion/cells are one natural example of this). In this case the number of electrons that flow does not translate proportionally to a voltage drop as is did in the case of the capacitor. That is why batteries often show almost constant voltage till when nearly "discharged", at which time the voltage starts to drop off quite quickly.

As to terms like in and out, higher and lower, these are all a matter of convention. The normal convention is that electrons are negatively charged and flow from negative to positive voltage, and current flows in the opposite direction to electrons i.e. positive to negative.

We also learned at school[wrongly] about current flowing in the opposite direction as electrons! While a flow of electrons actually is current flowing...thus one direction...from the neg of a battery through a conductor to the positive side.....Compare electrisity with say water.. it flows only from a higher to a lower pressure = difference in electron pressure[potencial difference] which is measured in "Volt". The amount of water flowing/second= Electric current [which is a flow of electrons] is measured in Ampere'. The amount of current flowing {Amps} = the difference in electrical pressure{Volts} devided by the resistance it has to overcome.

Does this answer the original Question?

{Dell I am not inglish speaking!}

Jurie

Think of a battery as a capacitor that has a very, very odd dielectric. The battery stores charge. The more charge, the higher the voltage (or, conversely, the higher the voltage, the higher the charge). Now, batteries tend to have almost the same voltage during a huge plateau for that charge/discharge cycle (remember the very, very odd dielectric!), but the idea is there.

no such thing as a volt. volt is a unit of measure which helps measure the effects of current or charge. ie my yard is 100 feet deep. well, what is a feet. current through resistance is a volt. looks like the current is decreasing therefore smaller current will give smaller volts.

the universe is green

It means the current in amps is exhausted...as there is no longer sufficient current to supply the voltage necessary, the battery is said to be dead...The current necessary is determined by the voltage required by the resistance of the circuit...