Why are my RV batteries not charging on shore power? Is the converter bad?
Sometimes, but it is not the first suspect. The converter turns 120V shore power into 12V to run the coach and charge the battery, and between it and the battery sit switches, fuses and lugs that fail far more often. Two meter readings tell you which side of that line the fault is on.
Reading 1: the battery, shore power off then on
Unplug, let the battery rest, and measure at the battery posts, not the cable lugs. A rested lead-acid battery reads about 12.6 to 12.7 volts full. Plug in and measure again. A working converter lifts it to its charging voltage, typically around 13.6 volts in float.
- Voltage rises: it is charging. If the battery still runs down, the battery itself is suspect, or it is lithium on a lead-acid profile (below).
- No rise: take the second reading.
Reading 2: the converter's DC output
Measure at the converter's 12V output terminals with shore power on.
Output present, battery not seeing it. The converter is fine; the path to the battery is not. In order:
- Battery disconnect switch. Many rigs have more than one, near the battery and inside by the door. One that is off isolates the battery while the converter keeps the coach running, which looks exactly like a failed charger.
- Main fuse or breaker at the battery. Test it for voltage on both sides; voltage on one side only means it is open. Replace it with the same rating, never a larger one.
- Reverse polarity fuses. Many converters carry one or two on their own board, separate from the branch fuses. They blow if the battery was ever connected backwards or a jump start went the wrong way. Test them; they often look intact when they are not.
- Lugs and ground. A corroded lug or a painted-over chassis ground reads fine at the post and passes nothing.
No output, with 120V present at the converter. Check the pedestal breaker, the coach's AC breaker and any tripped GFCI first. If 120V is reaching the converter and nothing comes out, the converter has failed.
If the battery is lithium
A converter built around lead-acid sits near 13.6 volts, and a lithium battery held there stops well short of full, so it can look like it is not charging. Check whether your converter has a lithium mode: see is my WFCO converter lithium compatible. Also check the BMS: a lithium battery refuses charge below freezing, and one that has shut down after a deep discharge reads near zero until it wakes.
If you replace it
A charger you can set to your battery's own voltages, such as the Blue Smart IP22, covers both chemistries. A SmartShunt then shows exactly what is going into the battery, so you are not guessing from voltage again. If nothing on 12V works at all, start with no 12V power in the RV.
Send us your readings from each step and we will help narrow it down. Everything ships from our warehouse in Upland, California.
What you need
Want the full walkthrough? Read the complete guide.