RV battery not charging when plugged in to shore power

Common symptoms

• The RV has been on shore power all night, and the house battery still reads the same as when it was unplugged.
• Lights are bright while you are plugged in, then fade fast as soon as you unplug.
• The battery monitor panel shows the battery low even though the pedestal is on.
• You put in new lithium batteries and they never seem to reach full.

Quick checks before anything else

• The battery disconnect switch is on.
• 120V outlets in the RV work, so shore power is really reaching the coach.
• The 120V breaker that feeds the converter is on. Push it fully off, then on.
• Battery cables are tight and free of white or green corrosion.
• Battery voltage, read before and after plugging in, goes up when you plug in.
• Flooded batteries have water above the plates.

What causes it?

• Battery disconnect switch off On many RVs the switch sits between the battery and the converter, so the converter runs the lights but cannot reach the battery.
• No 120V to the converter A tripped breaker, a dead outlet the converter plugs into, or a surge protector still holding power off.
• Blown fuse or loose wire on the battery side Reverse battery fuses on the converter, an inline fuse in the battery wire, a loose ground, or a corroded terminal.
• Failed converter It puts out zero volts with good AC in and good fuses.
• Worn out battery A shorted cell or a sulfated battery will not take or hold a charge, even from a healthy converter.
• Charger and battery mismatch A lead-acid converter on lithium batteries charges slowly or not fully.

Step-by-step: find why the battery won’t charge on shore power

When your RV battery is not charging when plugged in, the fault sits between the pedestal and the battery posts. We start with switches and quick readings, then test the converter, then the battery. You need a multimeter set to DC volts.

1. Take a resting battery reading Unplug, turn off 12V loads, and put the meter on the battery posts. Trojan Battery says to let a battery rest at least one hour after charging for an accurate reading. A fully charged 12V lead-acid battery at rest reads about 12.6 volts or a little more. Write the number down. You will compare against it.

   

2. Plug in and read again Plug in, wait for the surge protector delay to end, and read again. A charging battery reads higher than the resting number. A full battery on a WFCO or Progressive Dynamics converter sits near one of the converter’s mode voltages: 13.2, 13.6 or 14.4 volts. If the reading does not move at all, the charge is not reaching the battery, so go on to step 3.
3. Turn on the battery disconnect Find the battery disconnect switch. It may be a rocker switch by the door, a knob near the battery or a switch in a storage bay. On many RVs it cuts the battery off from the converter, so the lights work on shore power but the battery gets nothing. Wiring varies, so test it: switch it on, then repeat step 2.
4. Prove the converter has 120V Check that the RV outlets work. Then find the converter’s breaker in the 120V panel and push it fully off, then on. Some converters plug into a 120V outlet behind a panel, so check that the plug is seated. If no 120V outlet works anywhere, the problem is upstream: see RV has no power when plugged in.
5. Check the reverse battery fuses WFCO WF-8900 power centers have reverse battery protection fuses on the front panel. Progressive Dynamics converters have them too. Both makers say a battery hooked up backwards, even for a second, is what blows them. Look for a broken strip or use a continuity tester. Make sure the battery is wired positive to positive, then replace each fuse with the same type and rating.
6. Test the converter output This is WFCO’s own test, and it works on most converters. With shore power on, disconnect the cables at the battery. Put the red probe on the red (positive) cable and the black probe on the black (negative) cable. WFCO says a reading of 13.6 volts, plus or minus 0.2, with no load means the converter works, as long as the AC going in is 105 to 132 volts. Reconnect the cables when you are done.
7. If the test reads zero, check the wiring WFCO lists four things to check when the output at the battery reads about 0.0 volts: an open inline fuse in the battery wire (if the RV maker put one in), a broken wire between the converter and the battery, a loose ground, and connections that are not tight enough. If the fuses and AC power are good and the converter still reads zero, WFCO says the converter is not working. Our guide to an RV converter not working covers testing and replacing it.
8. Clean and tighten the battery terminals Corrosion and loose terminals block charging even when the converter is fine. Turn off shore power, take the negative cable off first, clean the posts and cable ends, then refit the negative cable last and tighten both.

   

9. Check water in flooded batteries WFCO says to check the fluid level in any battery on the RV charging system every month. Trojan says plates left above the fluid can be damaged for good, and to add only distilled water, best done after charging.
10. Test the battery itself If the converter passes step 6 and the cables are good, the battery is next. WFCO notes that a converter that keeps cycling between its normal and fast-charge modes can point to a shorted battery cell. With a hydrometer, Trojan says a reading of 1.277 or more means full charge for most of its batteries. A battery that will not reach full, or drops fast once unplugged, needs a load test at a battery or RV shop.

WFCO vs Progressive Dynamics: what changes

Both brands use the same three charge voltages. They differ in how much you can see and control.

WFCO WF-8900 series. The converter picks its mode by itself from the RV system voltage. Absorption, its normal mode, is about 13.6 volts. Bulk, its fast-charge mode, is about 14.4 volts for no more than four hours. Float, its storage trickle, is 13.2 volts, and turning on a light sends it back to normal mode. There is no light that shows the mode, and WFCO says the unit has no serviceable parts.

Progressive Dynamics with the Charge Wizard. The Charge Wizard is PD’s four-stage control. It uses Boost at 14.4 volts to bring the battery to about 90%, Normal at 13.6 volts, Storage at 13.2 volts, and Equalize at 14.4 volts for 15 minutes every 21 hours. A light and button, on the converter’s fuse board or on a plug-in pendant depending on the model, show the mode and let you force Boost by hand. In PD’s own test, a 55 amp converter brought a drained 125 amp-hour battery to 90% in about 3 hours at 14.4 volts, but needed 40 hours at 13.6 volts. So a battery sitting at 13.6 volts is charging, just slowly. PD9100 series units without the optional Wizard hold a steady 13.6 volts.

Lithium batteries. The voltages above are for lead-acid and AGM batteries. Progressive Dynamics sells separate two-stage models for lithium (LiFePO4) batteries and warns not to use those on lead-acid. If you switched to lithium, match the converter to what the battery maker asks for. For both 12V and 120V power, see our RV electrical problems guide.

When to call an RV tech

• The converter reads zero at the unhooked cables with good fuses and good AC in.
• New reverse battery fuses blow again right away with the battery hooked up correctly.
• The converter’s 120V breaker trips again as soon as you reset it.
• Wires, fuses or terminals show heat damage, melting or a burnt smell.
• You would need to open the converter or power center, or work inside the 120V panel.
• A battery is swollen or hot, or keeps boiling off water on shore power.

Common questions