Originally Posted by SLCChris
Am I at risk of overcharging the battery, reducing it's life, if it's wired like what I wrote above?
An alternator will generally not fully top off a AGM battery so unless the regulator fails for some reason, it shouldn't overcharge, rather it will always be slightly undercharged. Having a good 3 stage charger or solar to top it off will help a bit with longevity. The rule of thumb is never let the battery go below 50% (or about 12.2v) before recharging and top it off or charge it back with a smart charger.
Some people run a inverter off the alternator that powers a 3 stage smart charger so when driving down the road the house battery is brought back up with a good clean charge. The inverter must be connected to the ignition so when the engine is shut down the inverter turns off or you'd end up with a dead starting battery. If I did something like that, I'd want a A/B switch so I could cut in the alternator if needed.
The bad thing about many of the converter/chargers out there are they usually have poor battery chargers in them so a good 3 stage charger is a better choice.  There might be quality converters available and many high end inverters also have multi stage chargers built in them but they can be expensive.
You can google 3 stage chargers and read how they work. Stay away from standard garage chargers if you want to get the most life out of your battery.
Quality in batteries is usually in the lead that is used. Lifeline/concorde are some of the best but Deka, odyssey, and a few other make high end batteries.