Most RVs use a converter/charger to turn 120-volt AC shore power into roughly 12-volt DC power for lights, control boards and battery charging. Some rigs use an inverter/charger instead. When the battery continues to discharge while the RV is plugged in, work through the power path in order. Guessing at the converter before confirming its input can waste time and money.
1. Confirm that shore power is actually reaching the RV
Check whether known 120-volt loads work, such as a standard receptacle or microwave display. Reset the pedestal breaker and the RV main breaker by moving each fully off before switching it on. Inspect the shore cord, adapters and inlet for darkening, looseness, melted plastic or unusual warmth. A 50-amp RV can lose one hot leg and still appear partly powered.
If an electrical management system is installed, read its display. It may intentionally block power for low voltage, high voltage, open neutral, reverse polarity or a built-in start delay.
2. Measure the battery at rest and while plugged in
With the charging source off and the battery rested, measure directly across the battery posts—not the cable clamps. A fully charged lead-acid battery is commonly near 12.6 volts at rest, while a deeply discharged one may be close to 12.0 volts. Battery chemistry, temperature and recent charging affect the exact reading.
Connect shore power and wait several minutes. A working charger should normally raise voltage above the resting level. The exact target depends on battery chemistry, charger profile and charging stage. If voltage does not rise, continue upstream. If voltage rises at the converter but not at the battery, suspect a fuse, breaker, disconnect switch, cable or ground connection.
3. Check the converter’s AC supply
Find the converter or inverter/charger using the owner documentation and equipment label. Verify its branch breaker is on. Some converters plug into a receptacle that may be protected by a GFCI. A tripped upstream GFCI can silently remove charger power while other RV circuits continue working.
Listen for the cooling fan, but do not treat silence as proof of failure; many fans run only when temperature or load requires them. Confirm ventilation openings are not blocked by stored gear.
4. Inspect the DC charging path
Turn off and isolate power before handling fuses or cables. Check the battery-disconnect switch is in the use or on position. Inspect the main fuse or resettable breaker near the battery and the reverse-polarity fuses specified by the converter manufacturer. Replace a fuse only with the same type and rating. A replacement that opens again indicates a fault that needs diagnosis.
Inspect battery terminals and frame grounds for corrosion, looseness and heat. High resistance can allow a meter to show voltage with no load while preventing meaningful charging current.
5. Separate a charger problem from a battery problem
A damaged battery can pull charger voltage down or appear charged immediately while storing very little energy. Charge the battery fully with a known-good, chemistry-compatible charger and have it load or capacity tested. Batteries in a series or parallel bank should be inspected individually and as a complete bank.
What the results usually mean
- No 120V at the charger: trace the breaker, GFCI, transfer switch or shore-power path.
- AC input present, no DC output: the converter/charger, its configuration or protective fuses may have failed.
- Charging voltage at converter but not battery: inspect disconnects, main protection, cables and grounds.
- Charging voltage reaches battery but runtime is poor: test battery capacity and unintended loads.
Want a diagnosis tailored to your symptom?
Use the electrical walkthrough to narrow down battery, converter, fuse and shore-power faults.
Start electrical troubleshooter →When to call a professional
Stop for hot cables, swelling or leaking batteries, repeated fuse failure, burned connections, unstable shore voltage or any test that requires opening a live distribution panel. Inverter/chargers can involve both high DC current and lethal AC voltage.
Sources and review notes
This guide is general owner education. Specifications and procedures must be confirmed with the manuals for the installed battery and charger. Safety framing was reviewed against general guidance from NFPA electrical safety resources and manufacturer-first diagnostic practice.