Energy would be expressed as a power-time product, ie watt-hours, not power only (watts).  

But anyway, by your numbers the nominal battery capacity is 1320 watt-hours, or 1.32 KWH.  If you can really add/remove this amount of energy 800 times, then your total storage/release capability of the battery over it's useful life would be 1056 KWH.

In reality, if this is a typical garden-variety "deep-cycle" battery, the specs are not always as they seem.  The capacity of 110 amp-hours may be specified at a fairly low discharge rate, typically C/20, or 5-1/2 amps in this case.  Higher discharge rates will result in lower capacity before recharge is needed.  Also, if the maker specifies an 800-cycle life, it is probably referenced to a much lower depth of discharge.  If you really use all the capacity between recharge cycles, then your battery lifetime (total # of cycles) will be much less.  Finally, the capacity will also decrease with usage.  Capacity after several hundred moderately-deep cycles may be substantially less than 110 AH.

 110 Amp Hours * .20 = 22 Amp Hours

If the average voltage during discharge is 12 Volts (of course it actually varies) then one can estimate the average Watts taken out per cycle.

 22 Amp Hours * 12 Volts = 264 Watt Hours

If the average Watt Hours removed is 264 and the number of lifetime cycles is only 800, then the total Watt Hours removed would be:  

 800 Cycles * 264 Watt Hours = 211200 Watt Hours, or 211.2 Kwh

You have opened a real "can o' worms" here. It depends on a lot of variables.

One would need to get some sort of feel of how much energy was in at each particular point in time. This will mean getting a discharge curve. To get close to this one would  plot energy and time on a graph. One would start with the 12.8V (just a guess) and discharge with a constant Ohm load. As time increased and energy drained one would plot the curve and have a spreadsheet program get a time/voltage graph.

This would give one an idea of the point in time of a 'new' battery. As the battery aged, new graphs would need to be built. After all this work, one would get a new progression/regression curve and finally a master formula for the power.

This curve could then be 'Integrated' over the time span and give an approximation for your particular case.

Enjoy,

as the others have stated there are many variables.

in general you will get more kwatt/hrs out using a specific discharge/charge regime.
if you can work within those constraints you can maximize the life of the batteries or get more kwatt/hrs out over their lifespan,but not both.

so it all comes down to what you want or need from your batteries.

for instance, keep them cold and they will last longer, with lower capacity.
keep em hotter and they will deliver more, but at a reduced lifespan
and the list goes on.

having a clear understanding of all the variables and how they effect the battery
lifespan will dictate which method you use to get what you need or want out of them.

or at the very least have a reason to believe you will :)

otherwise it can be a crap shoot