Why all the worry about charging your house batteries back up when they hit 12.2 volts?
Lifeline says 10.5 volt is fully discharged.
From their site:
"As a battery chemically transforms from fully charged to discharged, it's voltage drops from 13.5 - 10.5 volts for a 12 volt battery. As the voltage drops this affects the amount of amps required to drive a load. (Watts law: amps x volts = watts)
13.5 volts x 10.00 amps = 135 watts
10.5 volts x 12.86 amps = 135 watts
As such, this calculator is for sizing purposes only. All systems should be thoroughly tested as they are installed to insure that the battery bank is appropriate for the load on site.
AGM Batteries are not harmed by high amperage charge and discharge so long as the input voltage is carefully regulated.
Charge 12 volt batteries at 13.2 - 14.4 volts
Ratings: Capacity ratings are after 15 cycles and are at 77°F (25°C) to 1.75 volts per cell.
What depth of discharge should be used when sizing a battery?
To get the best cycle life, the average depth of discharge should be as low as possible. Concorde
recommends the average depth of discharge be no greater than 50% of the battery’s 20 hour rating"
There are 6 cells in a 12 volt battery, so 6 times 1.75 is 10.5 volts. This is how they measure capacity. A fully charged battery is 12.6 volts. If you recharge at 12.2 you have used but 45% of the capacity you have paid for.
From the Lifeline site they want the AVERAGE discharge to be 50% which is 12.13 volts, there is no harm in occasionally going as low as 10.5. If we are dry camping I do not worry about it overnight, if it is low in the morning we fire up the generator for a while
I routinely let mine run down to 11 volts before starting the generator if we are dry camping. 12.2 volts is not some kind of drop dead number like that last 1.0 gallon of diesel in the tank.