Aside from having actual datasheets, a good rule of thumb for me seems to be comparison of the costs. Two batteries rated at 50AH, and all other things claimed equal, yet one is significantly cheaper, beware the 'free' capacity.

This becomes a real pain in the @$$ when youre dealing with a used battery too; trying to determine what it's actual capacity should have been isn't always discovered accurately by reading the label.

A good rule is to never design with an equipment requirement:battery capacity ratio of more than 50% of what the label on the battery indicates you can expect. This way, regardless, you stay inside the safe range of discharge level.

Not exactly a direct answer, but hopefully helped?

If you actually do that to a lead acid battery more than once or twice, it will ruin the battery.

from many sources

a flooded lead acid battery will return the most for your investment in watt/hrs
if not allowed to cycle below 50% (although a few deeper discharges along its life is not going to drastically reduce its life), and then the question becomes what is the most efficient charging regime for this type of battery and service.

again from many sources

charge daily or every other day from 50-80% of capacity, State of Charge
the lead acid battery can take alot of current between 50 and about 80% before it
starts to gas and the rate must be reduced.

so,,

charge daily from 50-80% state for charge, but what about sulfation?
sulfation is a normal function of the discharge cycle, you cannot escape sulfation
but you can do something so as not to allow it to crystallize and harden. That being
topping off the battery from 80% to full charge once every week to 10 days.

so where does all this lead you?

if you figure on charging once per day and your needs are 300amp/hrs daily
you will need a battery bank of approx 1000amp hours, that way you can work the 300amp/hrs from the 50-80% state of charge daily without getting into much deeper discharge.

if you are only going to recharge once every other day, your needs double to 600amp/hrs and so does the bank overall size, it goes up to 2000amp/hrs.

the next issue is charging capacity, to do it economically with an engine driven genset, you will want a capacity of approx 25% of battery capacity in amp/hrs
therefore a 1000amp hour battery bank will need approx 250amps of capacity, a larger 2000amp/hr bank will require 500amps of capacity to do it efficiently and
keep run time to a minimum,, however these are very large charging capacities
which most folks don't have... so you end up running proportionately longer to get the same amount of amp/hrs back in.

basically don't put in a 2000amp hour battery bank that you are taking more than 30% out of on a daily basis if you have only a 50 or 100amp generator,, it will be running all night just to get you ready for the next day. (actually it is likely it will be running virtually 24/7 trying to keep up.

clearly the lesson here is conservation, if you don't burn it, you don't have to provide storage capacity for it, or in turn provide charging capacity to keep the battery bank in shape.

hope that makes sense?

there are a couple of very good books commonly available on ebay

"wiring for 12 volts" and
"living on 12 volts"

even if you plan for higher voltages such as 24/48 the info is very good.

Getting a little back on track, though, here's my situation which isn't your typical solar powered home setup.

Basically, I want to be able to run my ham radios off battery power during periods of blackout- emergencies or even just lightning hitting a tree in the neighborhood. I've got two radios that can be run directly off the battery with some optional equipment that would need AC, but nothing that my little 100W inverter can provide and even those items would only be used once in a while. So, for all practical purposes I can run the whole thing off the battery.

Now, I'm obviously on the grid for everything else in the house and even the radios can be switched to grid power by simply switching two power cables. I can run off the grid or battery as needed. What would be the best way to run in order to maintain the life of the battery? Only use it every so often or use it all the time, making sure to keep it from getting below some percentage?

The battery I have is a Trojan 31-AGM. It's listed as a 110AH unit, but when you look at the spec sheet for it that is the peak AH rating. It says it's only good for 83AH if you're running it at a 5 hr rate and 110 if you're using it at a 20 hr rate. They don't even list 100 hr ratings for this one like they do for some of their other models, but their capacity ratings also say I can draw 25A for 3:10, which pretty well matches up with the other numbers. So, if I do my math correctly, I can draw about 5A off it for 20 hrs or about 17A off of it for 5 hours before it gets drawn down to 1.75V per cell. That's the spec they give as for how they determine the AH rating.

See, that's where my initial question came in. If they rate it as 110AH (assuming I'm drawing 5A off it it) they are basing that rating on the assumption that it will put out that much until it gets to a voltage that's 25% below full voltage. Therefore, I should be able to use the full 110AH rating in my calculations, right? It sounds to me like they are already accounting for the fact that it shouldn't be drawn down too far.

For charging it, I have a small solar panel now (with plans for a bigger one), but mostly I will be using a fancy grid/generator powered battery charger that is designed to properly charge and maintain AGM batteries.

My estimate is for an average draw during power out situations would be somewhere in the neighborhood of 2-3A, factoring in a typical draw of 1-2A with occasional draws of 10-15A while transmitting on the big radio. That ought to give me a good day and a half without any charging at all off of just the one battery.

Also, my neighbor has 8 L-16 batteries in a 12 volt system, how many watts of panels would he need to be a balanced system?  The houses are in the desert of Arizona.