Monday, June 5, 2023


‘But it worked yesterday!’ RV ‘Gremlins’, Part 1: Lead-acid batteries

“It worked fine, then it didn’t, and then it did!”

By Dave Solberg
How many times have you had something in your RV not work out on the road only to take it to the dealership or service center and pay them to tell you it’s working fine?! It happens all the time. I call it the RV “Gremlins” of the industry!

According to the movie, Gremlins are mischievous creatures that were known to cause malfunctions in the British Royal Air Force clear back to WWII. See how it fits?

Gremlins hiding in the RV

There are several areas Gremlins hide in an RV: the 12-volt electrical system, appliances, 120-volt electrical system, and even in roofs. I know of owners that have had roof leaks only to take it to a dealership and get the entire roof resealed only to have it leak again… and again.

And how about those annoying refrigerators that won’t cool efficiently only to hit 34 degrees sitting in the service bay? We’ve all experienced some type of Gremlin in our RVs. It can be not only frustrating but expensive, as well.

12-volt deep cycle lead-acid batteries

Lead-acid batteries have been a frustration for years for RV owners and typically last about two years. However, they should last 5-6 years. The deep cycle batteries in your house system are designed to be drained down to approximately 50 percent of their amp-hour or power storage capacity and recharged either by a converter, inverter, or solar panels many times, or “cycles.” They are measured in amp-hours, which means the approximate amount of time they can provide power to 12-volt systems such as the lights, roof vents, water pump, and any appliance running on LP. Lead-acid batteries can only be drawn down about 50 percent of their capacity. For example, a Group 27 battery with 100 amp hours can only provide about 50 amp hours.

Lead-acid batteries are simply storage devices for power. As that power is drawn out of the battery, sulfur attacks the lead plates and coats them. If this coating is not removed during the recharging process, it gets thicker and eventually limits the storage capacity.

Traditional converters that are part of the distribution center simply start the charging state at 13.6 volts and then reduce to 13.2 volts when the battery reaches 12.6 volts. This is the voltage that the battery will no longer accept a charge, so it is a maintained state.

Distribution center

This is a typical distribution center with the circuit breakers for 120-volt applications and the converter is behind the grill at the right. This type of charge will not break up the sulfation and will limit the battery’s chemical-to-electrical conversion. Sulfation can also occur when a battery is stored without a full charge during the winter, as all batteries will experience a slight drain if not connected to a charging or maintenance system.

These batteries were in a 2015 Thor Challenger. You can see how swollen they are and how the posts are corroded. These batteries would not hold a charge for any amount of time. They are not the original batteries.

This unit came standard with a WFCO standalone converter that just did a 13.6-volt charge. So I would imagine the original batteries became sulfated and were changed out for these Interstate 6-volt batteries. And it looks like there were originally four 6-volt batteries, as the tray is designed for that.

Charging a lead-acid battery

To properly charge a lead-acid battery, your system needs a multistage charger that starts with a bulk or desulfation stage. That is a high-voltage charge that literally boils the acid and breaks up the sulfur. This also causes excess gassing and acid depletion. This means more maintenance and checking of each cell. Chargers like the Progressive Dynamics models with Charge Wizard, inverters with chargers, and solar panels with charge controllers all have multi-stage chargers that will properly charge and maintain a lead-acid battery.

RV Gremlins in the batteries

The Gremlin in this case is in the actual condition of the lead-acid battery. If the battery is sulfated, it can be charged to 12.6 volts, which is a fully charged lead-acid battery. However, it will drop fast and not provide the amp hours it was originally designed for. It also cannot be accurately tested by local auto shop and service center equipment.

According to my sources at Lifetime Battery, Trojan, and U.S. Battery, the only way to truly test a battery’s condition is to properly charge the battery and place it on a 25-amp load machine and verify how many hours it provides power, which almost never happens. And I get this all the time: “I had the batteries checked by a technician and they are fine.” Also, “The batteries are 12.6 volts so I know it’s not the battery.” And, “The batteries are only six months old and register 12.6 volts, so I know they are good!”

AGM and lithium

The hot button has been Absorbed Glass Mat (AGM) and even now lithium batteries. However, my contact at Trojan coined them “the lazy man’s battery.” Before shelling out the high dollars needed for AGM or lithium, I suggest getting educated on the proper charging and maintenance of lead-acid batteries, checking your fluid level regularly, and getting a portable battery booster. I have one that provides a 13.6-volt boost. I use it to connect to the house batteries when something is not working properly to verify it’s not the RV Gremlin in the house battery rather than the component.

More RV “gremlins” next Saturday. Stay tuned!

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook.” 

Read more from Dave here


Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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Brian Burry
11 months ago

The AGM Battery is the Smart Person’s Battery because it is engineered better than the lead acid battery! Not that much more expensive (I bought mine at Batteries Plus and they removed the old batteries and installed the new AGM Batteries for free with purchase), but the reliability is a peace of mind issue. Many RV’s are in storage more than used and with a trickle charger, AGM are dependable. Lithium Batteries may be too expensive for many, yet the small increase to upgrade to AGM is money well spent! We have a 2009 Newmar and we had our AGM batteries installed after a They-were-working-yesterday experience where going from California to Colorado we had an engine and transmission failure signals, that stuck us in 3rd with no speedometer or compression brake driving over and downhill in the Rockies! ALL DUE TO THE CHASIS BATTERIES Failure. When it was diagnosed as the batteries were the problem, that made up our decision to go smarter!

11 months ago
Reply to  Brian Burry

What is an AGM Battery? ( acronym “AGM” stands for “Absorbed Glass Mat,” which in the case of a lead-acid battery, means the electrolyte in the battery is absorbed into fiberglass matting in between the plates in the cells.”

Wayne C
11 months ago

Trojan contact coined lithium batteries “the lazy man’s battery”. Let’s see..lithium batteries don’t require water checks, periodic desulfation, or corrosion cleaned from the terminals. They will shut themselves off before discharging to a harmful level (therefore don’t require monitoring the voltage) which is after delivering twice the power of a similarly rated lead acid battery. They recharge much faster than lead acid batteries. In comparing power delivered, lithium is cheaper than lead acid. So yes, they are a “lazy man’s battery”. What was Trojans point?

11 months ago
Reply to  Wayne C

the tech probably doesn’t sell the lazy type batteries and loves the repeat business for lead acid customers

Dan Kruger
8 months ago
Reply to  Scott

It’s a man with a smart plan…..lazy has nothing to do with it…..lets see horse cart transportation to car I guess all who drive are lazy…..

11 months ago

What I have seen over a lot of years is the owner of an RV will have it parked in storage for many months with no electrical hook up that will maintain the battery charge. This is a killer of battery life with batteries lasting maybe 2 years. I am fortunate that I store our trailer indoors with it plugged in whenever were not using it. I have Lifetime 6 volt battery system (to 12 volt) and because I keep it charging at all time have to replace our batteries every 8 years. We camp a lot of boon-docking so were using the battery system a lot. Lack of proper charging is the biggest problem. One other thing I read the owners manual when we bought our trailer (2004) and it said if you bought an electrical module that plugs into the converter it would up the charge once a week to de-sulfur the lead plates.There’s different modules for flooded cell and AGM batteries and they work as advertised.

11 months ago

One of the biggest fallacies are “no maintenance” lead acid batteries. Our new coach came with 8 AGM batteries….no worries about acid discharge….and corrosion

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