Both circuits use the same float charging circuit. There is a 5 ohm, 5 watt resistor that limits the battery charge if the battery is deeply discharged. By adding more batteries, the recharge time will be increased but they will recharge over time.
The main thing to maintain is a power supply voltage output of `13.8 to 13.9 volts coming out of the power supply. Without the current limiting resistor and recharging a deeply discharged battery, the recharge current could exceed the battery recommendations for a short period of time.
If you deeply discharge a sealed lead acid battery and leave it discharged for more than several days, the battery may not recharge using a standard float charger that is available in most security and home automation controls. You can force a recharge by placing the battery on a variable power supply and monitoring the current flow into the battery. On a dead battery, raise the voltage until you see current flow start going into the battery of around 100 - 250 milliamps on a 4 to 8 amp hour battery. This may be 16 to 20 volts depending on the state of the batteries plates and how they have been oxidized. Very quickly the current flow will start to increase and you will have to lower the voltage. Keep lowering the voltage until you reach 14.5 volts. Let it charge for a couple hours then move the battery back to a float charge system or reduce the power supply voltage to 13.9 volts. This will maintain a float voltage on the battery.
The downside of recharging a deeply discharged battery:
Once a battery is deeply discharged and left that way for days, an oxidation layer starts to build on the plates. By raising the voltage you are burning through the oxidation layer and forcing current into the battery. You never totally erase the oxidation layer, so the current delivering capacity of the battery will never be as good as it was before being deeply discharged. This is why the Elk M1 has a low battery cutoff circuit built in. The low battery cutoff circuit prevents the battery from being deeply discharged and ruined.
The same chemistry is true for your car battery. If you run it down and leave it discharged for a long period of time, it turns into a nice boat anchor!