Freelheeler, don't mix and match batteries unless you isolate them. If they are in a combined bank they should be the same type and age.
Shall we dig deeper...?
So to explain my setup a bit more, the house battery SRM 27 (camper)is isolated from the starting battery (truck) using a solenoid, both charge from the truck. The goal being that driving a few hours per day charges the system and we're good for a night or 2. If i were to add a third battery (SRM24) to the system it would be to the camper. I was originally running only a SRM24 but it failed late last summer and Interstate honored the warranty so i paid the extra and bought a bigger battery. This also forced me to redesign my battery storage area to accommodate the larger size plus allow room for an additional SRM24 if i need it.
I attached the chart to get some help understanding and calculating, so let assume the freezer draws 1.5A continuously, the question= how long will it run? If i understand the chart the manufacture claims the SRM27 will sustain for 18.4 hours at 5A continuous draw which = 92 total useable amps, so at 1.5A continuous draw i should have approximately 61 hours of run time= 2.5 days?
PODS8, if i understand things correctly and i want to extend my run time i have a few options; one being to connect the house battery's in series (direct) which will require a second SRM27 ideally of the same age, or two use a solenoid to isolate the house battery's (SRM27 from SRM24). This in theory would give me an additional 86amps and a run time of 57 hours or just over 2 days. For a total of 4.5 days of continuous use.
I can see where this could becomes a real mind twister, add in lights, heater, etc. compounded by time of year, hours of day light, cold weather, warm weather and you end up with a real world guesstimate!