In our previous post on RV power converters, we discussed the differences between an RV power converter, an RV battery charger, and an inverter/charger. In our post on RV battery converters vs. chargers, we provided some details about the differences between the two. Because all these different devices and their uses can be confusing, we’re dedicating this post to focus on the RV battery charger, in the hope that it will clarify the importance of proper charging for lead-acid batteries, whether they’re flooded, gel, or AGM.
We know that many RVers use lead-acid house batteries (they’re readily available and, by far, the cheapest option). We also know that even basic flooded lead-acid batteries aren’t cheap enough to be considered truly disposable. However, far too many people find themselves needing to replace them after a year or two of use due to poor battery management.
NOTE ABOUT LITHIUM BATTERIES: This post is all about properly charging LEAD-ACID batteries (like standard flooded lead-acid, AGMs, or gel cell batteries) and does NOT apply to Lithium chemistries (like the Lithium Iron Phosphate formulation most commonly used for RV lithium batteries). If your RV came from the factory with Lithium batteries, the charging equipment installed should be properly designed to handle them. If you are upgrading your RV from lead-acid to lithium batteries, please check out our article Upgrading Your RV To Lithium Batteries Can Require More Than You’d Think!
That’s why we hope this post will help clarify how to properly charge and maintain lead-acid RV house batteries, ensuring they provide reliable power and have their optimal lifespan. Before switching to lithium batteries in our (old) motorhome, our lead-acid batteries lasted 7 years (of full-time use with lots of dry camping/boondocking). We hope yours will last at least that long, too. How? Proper charging and maintenance. Let’s keep going…
What Is an RV Battery Charger?
An RV battery charger is designed to replace the energy removed from the battery during use, for dependable service and long life. However, not all battery chargers are the same, and ensuring that your batteries are being charged properly is critical to preserving them.
Different types of battery chargers charge batteries in different ways. However, if you have lead-acid batteries (regular flooded, gel, or absorbed/absorbent glass mat), there’s one type of battery charger that’s far more likely to properly maintain and preserve the life of your batteries. Newer smart chargers enable the RVer to select the appropriate type of charging for the specific type of batteries they have, ensuring optimal charging occurs in stages as it should.
This is an older 2-stage converter charger in a 1998 Roadtrek Class B RV. A 2-stage charger doesn’t provide optimal charging to today’s batteries.
Side Note: Confused about RV batteries in general? Check out our RV battery article for a guide to the various types of batteries and their differences.
What Are RV Battery Charging Stages?
First, let’s clarify one important thing — we’re talking about RV house batteries here, not chassis batteries. Chassis/starting/engine batteries start a motorhome’s engine and then stay charged by the alternator all the time. RV house batteries are deep cycle, designed to be drawn down (with limitations), then recharged (that down and up is the “cycle”) as part of regular usage.
House batteries power all of your RV’s 12V DC equipment — including the water pump, fans, interior lights, and more. They can also power 120V AC appliances (such as your microwave, coffee maker, and hair dryer) through the use of an inverter. All of these power draws, and repeated draining and charging cycles, are why an RV’s deep-cycle house batteries need to be charged in “stages” — and that’s what we’re covering today.
A charger (or converter/charger) may offer 2-stage or 3-stage charging. The charging stages are (voltages are listed for standard 12V flooded lead-acid batteries for example purposes only):
- Bulk Charge: The first stage of charging in which a high amperage charge is supplied to the battery bank. This stage typically returns 70-80% of the depleted battery capacity. It ends when the battery voltage rises to approximately 14.6V
- Absorption/Acceptance Charge: Once the Bulk Stage ends, that voltage (14.6V) is held steady while the charger slowly reduces the amperage being supplied. This stage returns the remaining 20-30% of depleted battery capacity and ends when the charging current has reduced to approximately 1% of the battery’s capacity (for instance, a 100 amp-hour battery would be fully charged when the Absorption charge current comes down to 1.0 amp, which is 1% of 100)
- Float Charge: Once the charging amperage drops to its defined target rate (again, typically down to 1% of the battery bank’s storage capacity in amp hours), charging voltage is reduced, usually to about 13.6V, to maintain the battery’s charge at 100% of its capacity.
How Do Different RV Battery Chargers Work?
Let’s take a quick look at the different types of battery chargers and the charging technologies they can provide for your RV batteries:
Single-Stage Chargers
Single-stage RV battery chargers are generally cheaper and use, as the name implies, a single-stage charging cycle. These typically supply a constant charging amperage until the battery bank reaches a set voltage, at which point they shut off. Completely. This is not the optimal way to charge and maintain deep-cycle RV batteries for long life. Single-stage chargers are usually found on older rigs.
Two-Stage Chargers
Again as the name implies, 2-stage chargers replace the battery’s energy in two steps. First, the charger supplies a Bulk charge, and then it tapers off to a Float charge. There is no Absorption Stage (so a significant amount of the battery’s capacity isn’t being replenished). In effect, it does the same as a single-stage charger. However, once the battery is fully charged, it returns to a lower, variable amperage to maintain the battery’s charge.
When shore or generator power is supplied, a 2-stage charger will start in Bulk mode, supplying its maximum amperage until the battery’s voltage reaches its target set point (approximately 14.1 to 14.6 volts for flooded lead-acid batteries). Once that voltage is reached, the charging current is stopped and the battery voltage is allowed to drop to its “Float” level (13.6 volts). The charger will supply current as needed to maintain the battery at 13.6 volts.
So, 2-stage chargers supply either full amperage to the batteries or just a Float charge to them. Again, this is better than single-stage charging, but the problem is that 2-stage chargers never completely charge a battery to its full capacity, because the Bulk stage can only return about 80% of the depleted charge, and there is no Absorption stage to complete the process.
All of this tends to increase sulfation on the lead plates contained in the batteries, which then shortens their lifespan. Like single-stage chargers, these are often found in older RVs.
Three-Stage RV Battery Chargers
Three-stage charging is really what’s needed to provide a complete recharge for deep cycle RV batteries. A 3-stage charger offers charging in (1) Bulk, )(2) Acceptance/Absorption, and (3) Float stages. These chargers start out in Bulk mode, just like a 2-stage charger does. However, once the battery voltage rises to its target level (in the range of 14.1–14.6 volts), the charger will then hold that voltage while it slowly ramps the charging amperage down.
This is a modern 3-stage converter/charger that will charge an RV’s batteries optimally which is beneficial to the health and longevity of the batteries.
This step, the Acceptance/Absorption stage, returns the battery to 100% full. Once the battery is fully charged, the voltage is then reduced to a Float level (typically around 13.6 volts), and low-current charging is supplied to maintain that voltage level (and help replace any power that’s actively being used in the RV for 12V appliances/functions). This more thorough charging process extends the battery’s lifespan and eliminates the potential for overcharging. Most lead-acid battery manufacturers recommend a 3-stage charging process to restore batteries to full capacity and extend their useful life. Of course, even well-maintained lead-acid batteries occasionally require equalization.
What Type of Battery Charger Can I Use In an RV?
Both built-in and portable battery chargers can be used on RV batteries, although they serve different purposes:
Built-In Style Chargers
An RV battery charger will often be incorporated into the RV’s “Power Center” module, complete with all the necessary 120V circuit breakers, 12V fuses, and the battery charger itself.
As we noted in detail in our post on RV power converters, many RVs have a converter/charger. This combination device provides both a converter (which changes 120V AC shore/generator power into 12V DC power for supplying electricity to the onboard loads) and a battery charger (often multi-stage to ensure proper charging). While functionally similar (both take 120V AC power and convert it to 12V DC), the primary difference between the converter and charger lies in their ability to control their output voltage and amperage:
- a CONVERTER supplies amperage at a fixed voltage (typically 13.6 volts), but that voltage can drop/sag if the amperage/power demand is more than the converter can supply. A converter CAN provide a slower charge rate than a charger, but if left connected for too long, it could result in overcharging the batteries.
- As noted in the section above, a CHARGER can provide amperage at varying voltages, based on the battery’s state of charge. WFCO, Progressive Dynamics, and PowerMax are reputable names in battery chargers and converter/chargers.
- BUY THE BRAND OEM'S USE - Trusted & Preferred more than 4-to-1by OEM’s. WFCO is the RV industry’s leading brand for power products. Relied on for...
- PATENTED AUTO-DETECT TECHNOGOLY - (Patent #12,113,377) ] Makes battery setup simple and seamless. Auto-Detect automatically recognizes and adjusts to...
- Includes built-in Charge Wizard.Fit Type: Universal Fit
- Reverse battery protection prevents damage from improper battery lead connection
- 🔋 PowerMax PM4 55A Converter for RVs & Boats – This 12V AC to DC power converter is perfect for powering RVs, boats, cars, solar systems, and...
- 🔋 Adjustable Output Voltage – With an output range of 13V to 16.5V, this converter is compatible with lithium, AGM, gel, and lead-acid batteries...
Portable Trickle Chargers
Trickle chargers (especially “Smart” trickle chargers) are appropriate for maintaining an already-charged battery while your rig is in storage. However, these generally aren’t suitable for day-to-day use to properly recharge an RV’s house battery while it’s in use. Trickle chargers are typically portable units like these:
- MEET THE GENIUS10 — Similar to our G7200, just better. It's 17% smaller and delivers over 115% more power. It's the all-in-one charging solution...
- DO MORE WITH GENIUS — Designed for 6-volt and 12-volt lead-acid (AGM, Gel, SLA, VRLA) and lithium-ion (LiFePO4) batteries, including flooded...
- Stay Charged: The 10 AMP car battery charger automotive provides a full charge to your machine's battery before automatically switching to float mode...
- Connect and Forget: With a low maintenance design, our universal vehicle charger and maintainer is compact, lightweight, and easy to operate even in...
Bottom Line About RV Battery Chargers
The most important thing to remember about battery chargers or converter/chargers for lead-acid RV house batteries is that 3-stage models are best suited for providing proper charging, maintenance, and a long lifespan. While any battery charger may automatically charge your batteries, 3-stage chargers/maintainers are the best option for doing the job correctly. They provide the Bulk, Absorption, and Float charging stages that are necessary to maintain your battery’s optimal health over the longest period.
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Joel Prah
Monday 6th of April 2026
Hi Guys, I have a 2008 Bigfoot slide in truck camper. It has a Parallax 45A Model 7345. Do you know how many stage this might be. The manufacturer (Bigfoot) is suggesting replacing the 12v section unit with a Progressive Dynamics replacement. We are having problems with charging the house batteries while driving with our truck, which is a 2021 GMC 1 ton. What do you recommend we check or change in regards to this charging issue. We winter camp and boondock, and our solar does a good job, until we have several days of snow or clouds. Thanks for any help.
TheRVgeeks
Tuesday 7th of April 2026
Hi Joel. Looking up that Parallax charger, it looks like it's a single-stage unit, so upgrading it with a Progessive Dynamics model that's a 3-stage charger will definitely help improve the battery life for your camper's battery(ies). As far as charging while driving the truck, we don't have a lot of experience with how truck campers are usually wired for this. Our guess is that they rely on the same small-gauge wiring from the truck camper's 7-pin plug... which isn't going to allow very much charging power through. The best bet may be to custom wire a DC-to-DC charger between the truck's battery and the battery bank on the camper.
Check out this article from our friends Tom & Cait Morton about how they set up their truck camper to charge a large lithium battery bank. Even if you don't have a large bank like that, it will give you an idea of how to wire up a system like it:
https://www.mortonsonthemove.com/truck-camper-lithium-alternator-charging/
Ken Arnold
Monday 14th of July 2025
As a long time reader of your newsletter and viewer of your videos, I have to commend your outstanding contributions to the RV community! That said, now that high quality Lithium Iron Phosphate batteries have come way down in price ($200 for high quality 100Ah unit), the charging of those types should be included in your article, especially since they are far superior to lead-acid types in almost every way. Nowadays it hardly makes sense to buy lead-acid units when replacement is needed. But the Li charging profile is much different as I'm sure you're aware since you have used Li batteries for some time now.
Let me know if I can help to update this post accordingly.
Cheers, - Ken
TheRVgeeks
Tuesday 15th of July 2025
Thanks for the kind words AND for the reminder about the prevalence of Lithium batteries, @Ken. We've updated the article to make sure that people are aware that the article applies to lead-acid batteries... and added a link to our article about the other charging & system components that may need to be updated to make the switch to Lithium (Upgrading Your RV To Lithium Batteries Can Require More Than You’d Think!).
Jim Wijnhamer
Tuesday 18th of March 2025
How do I know the amperage of my RV Converter? Thank you
TheRVgeeks
Tuesday 18th of March 2025
Hey Jim. You'll have to do a bit of sleuthing. You can:
Look at the unit itself and try and see a label or model number (from there, you can look up the specs). This, of course, requires you to be able to access the converter itself, which sometimes can be difficult (manufacturers tend to bury them). Look in your owner's manual and/or contact your RV manufacturer to ask. Check your 120V breaker box for the RV... there should be a breaker labeled for the "Converter" or "Charger"... check the amp rating stamped into the small face of the breaker switch... it should be rated to match the amp capacity of the converter.Hopefully one of those options will work for you!
Matt
Monday 15th of July 2024
My Magnum MS-2012 has a 4th stage. A "full charge" stage that completely turns off the float charge for up to 4 hours or when the voltage drops below the 13.6. Then in addition, it has an Equalization setting that will automatically control that process. Makes it super easy to complete this function annually - in my case.
Smitty
Tuesday 18th of July 2023
Good coverage/info of this area of RV'ing that can be confusing at times! On the Maintainer side of batteries. I'm probably no different then many RV'er's, and accumulated numerous Battery Minders and Tenders over the years, for different battery support. I think my favorite due to flexibility and ease of use, and lifting above it's weight with the 8A option, is the Battery Minder 128CEC (I have the older unit, now they call it the 128CEC2.). While our coach is in storage, on a 15A outlet, I'm able to maintain X's 6 8D FullRiver AGM's successfully, on the 4A setting. (We have dual 3K inverters, and I only leave the Inverter feeding the Refrigerator on. And the 4A supports the inverter overhead, and 22' Amana fridge demands, keeping the battery bank up. For chassis, X's 2 8D LifeLines - I use a smaller Battery Minder. Which also works well (Can't recall the model...). --- Curious of your thoughts on Desulfator's. Many consider the snake oil, others seem to swear by them... The 128CEC series has this... Opinions on this function would be appreciated. - Best, and travel safe - Smitty
rag_ftw
Monday 15th of July 2024
@TheRVgeeks, I don't have any scientific proof but I do have data from my 4 Trojan 125s. The last set lasted 9 years when maintained by a Battery Minder 128CEC. I only allowed the Xantrex to charge them when driving down the road. I believe they would have lived longer if my automatic watering device had not failed on one and allowed one cell to run dry. I can also say my lawnmower batteries last for 5-6 years when maintained by a Battery Minder with the desulfator mode. I too would like to see some 'hard data' concerning desulphating chargers.
TheRVgeeks
Wednesday 19th of July 2023
Hey Smitty. Thanks for sharing your experience with chargers.
We're sort of on the fence when it comes to the "desulfator" modes. SEEMS like snake oil (i.e. too good to be true), but we've read of lots of people who swear by them. Of course... that's all anecdotal... we haven't seen any scientific proof/evidence to support that. Since we don't have a charger that has that function (and now have Lithium batteries that don't need it), we can't report from personal experience.
But, that said, we don't see how it could HURT... so we'd likely use the feature if it was available to us.