RV battery not charging? Here's the fix.

Dead house batteries take down your lights, furnace, slide motor, and water pump in one shot. Here's how to figure out if it's the battery, the converter, or something in between.

An RV house battery that won't hold a charge, won't charge on shore power, or drains overnight is one of the most frustrating problems because it affects almost every other system in the rig. This guide walks you through the checks in the order a mobile RV tech would run them.

1. Measure resting battery voltage

Disconnect from shore power, turn off the battery disconnect if you have one, wait 10 minutes, then measure the battery terminals directly with a multimeter. Here's what the number means for a standard lead-acid or AGM battery:

• 12.6V or higher: fully charged
• 12.4V: about 75% charged
• 12.2V: about 50% charged (don't go below this regularly)
• 11.8V or lower: deeply discharged, may be damaged
• Below 10V: likely dead or shorted internally

Lithium batteries sit flat around 13.2V to 13.4V until they hit the low cutoff.

2. Is shore power actually reaching the rig?

Plug a phone charger into an outlet inside the rig. If nothing happens, 120V isn't getting in. Check the campground pedestal breaker, your surge protector, and your shore power cord connection. Your converter can't charge the battery without 120V input.

3. Check the battery disconnect switch

Most RVs have a battery disconnect somewhere: at the battery itself, near the entry door, or in a basement compartment. When it's in the "off" or "store" position, nothing can charge the battery. If you just got the rig out of storage, this is the single most common reason the battery isn't charging.

Flip it to "use" or "on" and try again.

4. Clean the battery terminals

Pop the battery cover and look at the terminals. If you see white or green crusty buildup, that corrosion is blocking current from flowing between the battery and the rig. Disconnect the battery (negative first), scrub the terminals with a wire brush and a paste of baking soda and water, rinse, dry, and reconnect (positive first).

Smear a bit of dielectric grease on the terminals after reconnecting to slow future corrosion.

5. Test the converter output

Your RV converter takes 120V shore power and turns it into 13V+ to charge the battery. With the rig plugged into shore power and the battery connected, measure the battery terminals again. You should see:

• 13.2V to 13.6V: float or maintenance mode (normal for a charged battery)
• 14.0V to 14.4V: bulk charging mode (normal for a discharged battery)
• Under 13V while plugged in: converter has failed or is disconnected

If you see 12.6V or less while plugged into shore power, your converter is not doing its job. This is usually a bad converter module or a tripped fuse on the 120V side feeding it.

6. Check the water on flooded lead-acid batteries

If you have traditional flooded lead-acid batteries (not AGM or lithium), pop the caps on top of the battery. The lead plates inside should be fully submerged in liquid. If any cells are dry or the liquid is below the plates, top off with distilled water only, never tap water.

A battery that has run dry may have permanent damage. Try charging it with water added and see if it holds. If not, it needs replacement.

7. Hunt for a parasitic drain

If the battery charges fine but dies overnight with no appliances running, something is quietly drawing power. Common culprits: propane leak detector, stereo memory, fridge control board, slide-out controller, or a stuck relay. LED light stuck on inside a storage compartment is a classic one.

Disconnect the battery completely overnight. If it holds voltage when disconnected but dies when connected, you've confirmed a parasitic drain. Finding the exact circuit usually requires a tech with a clamp ammeter.

When to call a mobile RV tech

RV electrical systems can bite you. Call a pro if you see any of these:

• Battery is hot, swollen, or leaking
• You smell rotten egg or sulfur near the battery (venting hydrogen sulfide)
• You found a parasitic drain but can't isolate which circuit
• The converter is melting or smells burnt
• Lithium battery showing fault codes or BMS errors

Open Camphost and tell it your location, it will help you find mobile RV techs in your area.

Frequently asked questions

Why isn't my RV house battery charging on shore power?

Either the converter isn't outputting (test with a multimeter at the battery, you should see 13.2-14.4V with shore power on), the battery disconnect switch is off, a fuse is blown between converter and battery, or the battery itself is sulfated and won't accept a charge. Check the converter output first.

How do I know if my RV converter is bad?

Test voltage at the battery with shore power on. A healthy converter shows 13.2 to 14.4V. Below 13V means the converter is failing or the battery is so dead it's pulling voltage down (disconnect the battery and retest). Above 15V means the converter is overcharging and needs replacement immediately to save the battery.

What voltage is a fully charged RV battery?

A fully charged 12V flooded lead-acid battery reads 12.6 to 12.8V at rest (no load, no charging, after sitting an hour). 12.2V is 50%, the lowest you should regularly discharge a flooded battery. 11.8V is dangerously low and damages the battery. Lithium reads flat at 13.2-13.4V across most of its discharge.

Why does my RV battery die overnight even when I'm not using anything?

Parasitic drain. Even with everything 'off,' the LP detector, radio memory, propane fridge control board, and slide controller all pull a small current. Old or sulfated batteries can't hold against this drain overnight. Use a battery cutoff switch when storing, and replace batteries that test bad.

Can I use a car battery in my RV?

Not as a house battery. Car (starting) batteries are designed for short bursts of high amperage and can't handle deep cycling, they'll die in a few months. Use a deep-cycle marine/RV battery, a true deep-cycle (Trojan T-105 type), or LiFePO4 lithium for the house bank.