Dave, at best I think this is an academic concern. If I'm reading your question correctly.
Look at your battery, or its paperwork. It should be rated in A/hrs. Amp/hours. If you have more than one battery on the same circuit, add those values. Example: my battery is rated at 130 amp/hrs. That means I can run a 1 amp load for 130hrs, 2 amp load for 65 hours, etc.
There are a couple reasons why this is not really reality based. First, as your battery ages it will no longer have the amp/hr capacity it did when it was new. Secondly, we almost never have a 100% charge on the battery. There is a point of diminishing returns that any charger
once the battery is above 90% charged. So most of the time we're not using the full capacity. Lastly as end user consumers, we cannot predict the effects of things like ambient temperature or battery voltage on an appliance's drain on the system.
The good news: get yourself a good quality voltmeter and wire it in where you can click it on/off to monitor
the voltage state of the battery. You're close to full when reading 13.8 to 14v and FND when it reads 11.5v I start charging
at anything approaching 12v.