RV Residential Fridge Battery Drain: Generator Usage in Hot Weather Explained

Quick Take

Helen, based on your 2017 Pace Arrow 38B situation with new AGM batteries dying overnight while only running a residential fridge and small Jackery, you likely don't need new batteries yet. Your AGMs are less than a year old and should easily handle an overnight load of just a fridge. Common causes include your inverter drawing excessive parasitic power or your charging system not properly topping off the batteries during generator runtime. Your residential fridge is a heavy power draw - typically 150-200 watts continuously - but with proper charging, your new AGMs should handle 8-10 hours of fridge-only operation without dropping below starting voltage.

Common Causes

A common cause in your situation is inverter parasitic draw. Many RV inverters, especially older units, can draw 20-50 watts just sitting in standby mode, which adds up over 8-10 hours. Combined with your residential fridge's 150-200 watt draw, you're looking at 170-250 watts continuous load overnight. If your batteries aren't getting fully charged during generator runtime, they'll hit their low-voltage cutoff by morning.

Another major factor is inadequate charging time or faulty charging equipment. Your converter/charger may not be bringing the AGMs to full capacity during the day. AGM batteries need to reach 14.1-14.4 volts to fully charge (check manufacturer specifications), and many RV converters only put out 13.6 volts in float mode. If you're only running the generator intermittently and not getting a full charge cycle, your batteries start each night already partially depleted.

Temperature also plays a role in Phoenix heat. While you mentioned 80-degree weather, battery compartments can get much hotter, and AGM batteries lose capacity as temperatures rise. At 100°F, your batteries may only deliver 85% of their rated capacity.

Preparation

Safety Warning: When working with batteries and electrical systems, always disconnect power sources and wear safety glasses and gloves. Battery terminals can cause severe burns or explosion if short-circuited.

Before spending money on new batteries, gather some diagnostic tools. You'll need a good multimeter to check voltages, and ideally a battery monitor or clamp-on ammeter to measure actual current draw. Check your battery voltage first thing in the morning before starting anything - if it's below 12.0 volts, that explains why you can't start the generator. Healthy AGM batteries should read 12.6-12.8 volts at rest when fully charged.

Locate your main inverter - it's likely a large unit mounted near your electrical panel or in a basement compartment. Check the model number and look for any indicator lights or displays. Many inverters have an "eco mode" or can be completely shut off when not needed. Also locate your converter/charger, which may be combined with your electrical panel or mounted separately.

Prepare to do some load testing by identifying everything that runs on battery power. Your residential fridge, any LED lights, the inverter itself, CO and smoke detectors, and potentially things like slideout motors or leveling jacks all draw from your house batteries.

Repair Steps

Safety Warning: Before working on electrical systems, ensure the generator is off and all power sources are disconnected. Never work on live electrical circuits.

Start by measuring your actual battery draw overnight. With everything off except the fridge, use a clamp-on ammeter on the main battery cable or check your battery monitor if equipped. You should see roughly 15-21 amps draw for just the fridge and inverter standby. If you're seeing 25+ amps, something else is drawing power.

Next, check your charging system. With the generator running and no major loads, your battery voltage should read 14.4-14.7 volts at the batteries themselves, not just at the electrical panel. If it's only showing 13.6 volts or less, your converter isn't properly bulk charging the AGMs. Many RV converters have selectable battery type settings - make sure yours is set for AGM, not flooded cell.

To isolate inverter parasitic draw, consider turning off your inverter completely during a test period when you don't need the fridge running. Most inverters have a remote switch or can be shut off at the unit itself. You'll lose all 120V power including to your residential fridge, so this test only works if you have a separate 12V refrigerator or can do without refrigeration temporarily.

If your charging system checks out, extend your generator runtime. Instead of intermittent running, try running it for 4-6 continuous hours during the day to ensure your AGMs reach full charge. AGM batteries can take 6-8 hours to fully charge from 50% capacity, even with a good charger.

When to Get Help

Call a professional if your multimeter shows battery voltage dropping below 11.5 volts overnight, as this indicates either massive power draw or failing batteries despite their age. Also get help if your charging system isn't putting out proper voltage after checking all settings and connections - this might require converter replacement or rewiring.

Regarding your EcoFlow Delta that didn't work, it likely wasn't large enough for your RV's 30-amp system and residential fridge startup surge. A residential fridge can draw 15+ amps on startup, requiring at least a 2000-watt power station. The EcoFlow would work better for smaller loads like charging devices and LED lighting. For your Phoenix boondocking needs, consider a larger lithium system or additional solar panels rather than another power station - your roof can likely accommodate 400-800 watts of solar panels which would significantly reduce generator runtime and provide a more sustainable solution for extended boondocking.