RV Battery Not Charging - Troubleshooting Guide

You plug into shore power, everything inside works, but the battery voltage keeps dropping. The lights dim at night. The water pump struggles. Something in the charging circuit is broken.

Here’s how to find it without paying $150/hour at an RV shop.

Start With the Battery

Before chasing electrical gremlins, make sure the battery itself isn’t dead.

Check voltage with a multimeter:

Voltage	State of Charge
12.7V+	Fully charged
12.4V	75%
12.2V	50%
12.0V	25%
11.8V or less	Dead/damaged

A battery sitting at 10.5V or below may have a shorted cell. No amount of charging fixes that — it needs replacement.

Battery Age

Lead-acid RV batteries last 3-5 years. Lithium batteries last 10+. If your battery is over 4 years old and won’t hold charge, replacement is likely the answer.

Check the Converter

The converter is the most common failure point. It takes 120V AC from shore power and outputs 13.2-14.4V DC to charge the battery and run 12V systems.

How to Test

1. Plug into shore power
2. Set your multimeter to DC voltage
3. Measure at the converter’s DC output terminals
4. You should read 13.2-14.4V

Results:

• 13.2-14.4V = Converter works, problem is downstream
• 12.0-12.6V = Converter isn’t boosting, check fuses or it’s failed
• 0V = No output at all, check AC input side and fuses

Converter Fuses

Most converters have fuses on both AC and DC sides. A blown DC fuse cuts charging but shore-powered appliances still work (they run on AC). This tricks people into thinking the converter is fine.

Pull every fuse and inspect visually. Better yet, test with a multimeter for continuity.

Check the Wiring Path

The charging circuit runs: shore power → converter → fuse panel → battery disconnect → battery.

Battery Disconnect Switch

Many RVs have a battery disconnect switch. If it’s off, the converter charges the fuse panel but not the battery. Flip it on and check voltage at the battery terminals.

Corroded Connections

Pull the battery cables and inspect the terminals. White or green buildup means corrosion is blocking current flow. Clean with a wire brush and baking soda solution. Apply dielectric grease after reconnecting.

Wire Gauge

The charging wire from converter to battery should be at least 10 AWG for runs under 15 feet. Undersized wire creates voltage drop — the converter puts out 14V but only 12.5V reaches the battery. Not enough to charge.

Solar Charging Issues

If your solar isn’t charging:

Check the charge controller. Most have LED indicators or a display showing charging status. No lights = no power input.

Check panel output. Disconnect the charge controller and measure voltage directly from the panels. You should see 18-22V (for a nominal 12V panel) in direct sunlight.

Check connections. MC4 connectors on the roof corrode over time. Moisture gets in and resistance builds up. Inspect and replace any discolored connectors.

Charging System Maintenance

Prevent charging problems with a 5-minute check before every trip:

• Clean battery terminals
• Check water levels in flooded lead-acid batteries
• Verify converter fan runs when plugged in
• Test battery voltage after 4+ hours on shore power
• Inspect solar panel connections if equipped

A $20 battery monitor installed at the panel saves guesswork. You’ll know state of charge, voltage and current flow at a glance.

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