An RV battery that won't charge has one of five causes: a failed converter/charger, a dead battery that won't accept charge, a blown converter output fuse, a failed solar charge controller, or (on motorhomes) a broken alternator-to-house-battery charging line. Start by measuring voltage at the battery with shore power connected — it should read 13.5–14.8V.
Tell our AI exactly what your battery voltage is reading — it'll pinpoint the cause and give you the fix steps for your specific RV.
Get Free Diagnosis →Before blaming the charger, verify the battery is actually capable of holding charge. A sulfated or shorted battery will never charge no matter how good your converter is.
Disconnect shore power and turn off all DC loads. Wait at least 2 hours (overnight is better). Then measure the battery terminals with a multimeter. Below 12.0V means it's been deeply discharged. Below 11.8V with no load almost always means the battery is failed.
A battery can read 12.6V at rest but collapse under load. A proper carbon-pile load tester applies a half-CCA load for 15 seconds. If voltage drops below 9.6V, the battery has lost capacity and should be replaced. Even most auto parts stores will load-test for free.
Flooded lead-acid RV batteries last 3–5 years. AGM batteries last 4–7 years. If your battery is approaching end of life, replacement is often the most cost-effective fix even if it still shows adequate voltage at rest.
The converter is the box (usually near the 12V fuse panel) that charges your house battery from shore power. This is the most common cause of a battery that won't charge while plugged in.
With shore power connected and the battery disconnect switch ON, measure voltage directly at the battery terminals:
This is the classic WFCO symptom. The fan runs (the control board works) but the power conversion section has failed diodes. You can buy a replacement converter board or the entire unit for under $100. WFCO, Parallax, and Progressive Industries are the main brands in RVs — all have drop-in replacements available.
Many "bad converter" diagnoses turn out to be a single blown fuse or corroded connection.
If you're boondocking and relying on solar, check these in order:
Class A, B, and C motorhomes charge the house battery from the engine alternator while driving. If your house battery isn't gaining charge on a drive:
| Voltage (at rest) | State of Charge | Action |
|---|---|---|
| 12.7V+ | 100% — Fully charged | Normal |
| 12.5–12.6V | 75–90% | Charge soon |
| 12.2–12.4V | 50–75% | Charge now |
| 12.0–12.2V | 25–50% | Charge immediately |
| Below 12.0V | Deeply discharged | Charge with desulfation mode or replace |
| Below 11.5V | Likely failed | Load test — usually replace |
Not sure which step applies to your RV? Tell our AI your battery voltage readings and it'll guide you to the fix.
Ask RV AI →If battery voltage drops overnight while shore power is connected, the converter has failed and is no longer charging the battery. The battery is powering all 12V loads while the converter does nothing. Test with a multimeter — it should show 13.5–14.8V at the battery with shore power on.
Yes, a standard 12V charger will work in a pinch, but use one with a "deep cycle" or "AGM" mode if your RV has an AGM battery. Regular car chargers charge too fast for deep cycle batteries and can reduce their lifespan. A smart charger with multi-stage charging is always better.
A 100Ah battery at 50% discharge needs about 50Ah of charging. A standard 45-amp converter delivers roughly 30–40 amps net (accounting for 12V loads). Expect 2–4 hours to reach a full charge from 50% discharged. From a deeply discharged state (below 20%), it can take 6–8 hours.
If storing for more than 2 weeks, yes. Most RVs have a parasitic draw of 20–50mA even with everything off — this can drain a 100Ah battery in 2–4 months. Either disconnect the battery or connect a trickle charger/battery maintainer.
RV AI Help provides general information only. Always verify safety-critical electrical repairs with a certified RV technician. Product links are affiliate links — we may earn a commission at no extra cost to you.