RV Converter vs Battery Charger: A Comparison Guide

Thet terms “RV converter” and “RV battery charger” are often used interchangeably, but what are the differences between an RV converter vs battery charger?

The term “battery charger” is pretty self-explanatory. A battery charger charges your RV batteries. But there’s a bit more to it than that. Likewise, an RV converter charges your rig’s batteries, but it does a whole lot more than that.

So, what are the differences between the two exactly? And do you need both?

What is an RV Converter?

First, a little history:

When converters were first introduced in the RV market, they didn’t charge the rig’s battery/batteries at all (because in those early days, RVs didn’t even HAVE their own batteries… they relied on the towing vehicle’s battery when connected). Instead, the converter was simply there to convert the 120V AC shore power to 12V DC to power the lights, water pump, vent fans, etc. when the RV was disconnected from its towing vehicle (we’ll dig a little deeper into older vs more modern converters in just a bit).

If you’ve seen our full post on RV power converters, you know that the job of a modern RV converter is to convert 120V shore power to usable 12v DC power and charge your rig’s batteries. This is why, these days, they’re most typically called a “converter/charger” since they include a battery charger along with the ability to convert the 120V AC power in your RV to 12V DC power for the onboard loads.

This piece of RV equipment does double duty, providing 12V DC power supply for the electrical loads while connected to shore power AND allowinh your 12V RV batteries to be charged when plugged into shore power. Both functions are critical to keeping your lights, vent fans, appliance electronic control circuits, and some other accessories working, whether you’re hooked up to shore power or while you’re off the grid (not connected to shore power or running a generator).

What is an RV Battery Charger?

As you might glean from the term “battery charger,” an RV battery charger charges your RV’s batteries.

Modern RV battery chargers use more advanced, multi-stage charging cycles that are designed to more completely (and efficiently) replace the energy that’s been used from the battery. This has the added benefit of more properly maintaining the health of the battery, increasing it’s service life so it doesn’t need to be replaced as regularly.

Battery chargers can be portable units you can move from one battery to another, stand-alone built-in models (often combined with a separate, dedicated converter module), combination converter/charger units that serve both functions from one device, or even combination RV inverter/chargers.

What Are the Differences Between an RV Converter vs Battery Charger?

The real difference between an RV converter and battery charger is found in their ability to control their output voltage/amperage.

At it’s simplest, a converter supplies amperage at a fixed voltage (typically 13.6 volts) to supply the needed power to onboard loads. However, the output voltage can drop if the power/amperage demand is more than the converter can supply.

Another difference between a converter and a charger is that a converter can sometimes provide a slower charge rate than a charger. However, if it’s left connected for too long, it could overcharge the batteries.

A battery charger, on the other hand, can adjust its output voltage & amperage according to the battery’s state of charge. A good 3-stage charger will cycle its output through each stage in order to provide the most thorough and safe charging, which will extend the battery’s life.

A lot of confusion has come in because of the combination of these two functions into single converter/charger units.

What’s the Difference Between Older Converter/Chargers and Newer Ones?

There’s actually a significant difference between older converter/chargers and more modern ones.

Older converters and chargers (sometimes called “single-stage” chargers) will top up your RV’s batteries while you’re plugged into a power source. They’ll also charge your batteries pretty quickly if you’re running on generator power.

However, the efficiency of older units is so poor that they can damage your batteries under certain conditions: for example, if you keep your RV plugged into shore power for very long periods of time, an older single-stage unit can overcharge the battery.

Newer units, on the other hand, charge better and smarter. Not only do they properly charge your RV batteries, they also provide the proper degree of charge, in stages.

What Are Charging Stages?

RV chargers (or converter/chargers) generally offer 2- or 3-stage charging.

For example, with a 3-stage charger, the charging stages for standard 12V flooded lead-acid batteries are:

Bulk Charging

This is the first stage of charging, which supplies a high voltage & high amperage charge to the battery(ies). This stage generally brings your depleted battery back to 70-80% of its capacity. The bulk charging stage ends when the battery voltage reaches about 14.6V.

Acceptance/Absorption Charging

Once the bulk stage has ended, that 14.6V is held constant while the charger slowly reduces the amperage it’s supplying. This stage returns the remaining 20-30% of depleted battery capacity.

Acceptance/absorption charging ends when the current has been reduced to approximately 1% of the battery’s capacity. (For example, if you have a 100 amp-hour battery, it would be fully charged when the absorption charge current is reduced to 1 amp.)

Float Charging

The float stage begins once the charging amperage drops to a defined target rate (typically down to 1% of the battery bank’s capacity), In this stage, the charging voltage is reduced to 13.6V to maintain the battery’s charge at 100% of its capacity.

Most lead-acid battery manufacturers recommend 3-stage charging as the best and most efficient way to recharge a battery back to full capacity while also extending battery life.

Some older RVs have only 2-stage (bulk & float) converters/chargers. The problem with these is that they never completely charge the battery to its full capacity. This is because, as we noted above, the bulk charging stage can only return about 80% of the depleted charge. Over time, this constant under-charging of the battery leads to sulfation and shorter life.

Another problem with 2-stage chargers is that, because they spend longer in the high-voltage “Bulk” phase, they tend to boil off the water from the battery’s electrolyte solution, leading to more battery corrosion and contributing to reduced battery life (if the battery isn’t properly maintained).

Do I Need a Converter/Charger When My RV Is Connected to Shore Power?

You absolutely do, for several reasons.

First, as we’ve already noted, if you don’t have a working RV power converter (or charger) onboard, your batteries will drain and you won’t be able to use any of your rig’s 12V accessories or appliances. (Remember that some RV appliances like refrigerators, water heaters, and your RV’s propane furnace use 12V power for their control circuitry, even if they’re propane appliances.)

It’s also essential to have at least one battery charged and in good condition in the system to act as a buffer to keep the power provided by the converter/charger “clean”, which is important to the health of the electronics in the system. If your RV battery were dead or inadequately charged, the charger would try to compensate by sending more power to it, which would be hard on the entire electrical system (fluctuations in system voltage due to the different charging stages can cause increased wear on wiring and circuitry). This is why you never want to use any type of RV converter charger without having a good battery connected to the system.

As a final note, if your RV’s converter were to fail and you wanted to temporarily solve the issue until you could replace/upgrade it, you could run to any Walmart or auto part store and buy a portable multi-stage battery charger like this one. At a minimum, it would allow you to continue enjoying your trip without worrying about your batteries dying… at least until you return home and can get the converter/charger repaired.

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