The first van I wired for a client, we pulled the old dual six-volt golf cart batteries and dropped in a 100Ah Battle Born without giving the converter a second thought. Three weeks later he called me confused because his battery monitor showed the bank never got above 92 percent state of charge, even after two full days plugged into shore power. The converter was the problem the whole time.
That is the trap. A lithium battery will physically accept a charge from almost any converter, so nothing throws an error, nothing smokes, nothing beeps. It just quietly underperforms, sometimes for years, while the owner assumes the battery itself is defective.
The quick version
- Most RV converters built before roughly 2018 were designed for lead-acid absorption and float voltages that are too low, or too high, for ideal LiFePO4 charging.
- A converter that never reaches at least 14.2V will leave a lithium bank chronically undercharged, often stalling around 85 to 95 percent state of charge.
- Some older single-stage converters push a constant 13.6V to 13.8V forever, which some LiFePO4 batteries will accept fine and others will barely charge from at all.
- Newer converters like the Progressive Dynamics PD9200 series and WFCO WF-9800 series have a lithium switch or dedicated lithium charge profile built in.
- If your converter is not compatible, the fix is almost always a straight swap to a lithium-profile converter, not a full rewire.
What “converter” actually means in this conversation
In RV terms, the converter is the box that takes 120V AC shore power or generator power and steps it down to 12V DC to run your lights, water pump, and charge your battery bank. It is separate from your inverter, which does the opposite job, turning 12V DC battery power into 120V AC for outlets.
Some rigs have them combined into one inverter-charger unit, like a Xantrex Freedom or a Victron MultiPlus. Others have a dedicated standalone converter, often a WFCO or Progressive Dynamics unit tucked behind a panel near the breaker box. That standalone converter is usually the piece people forget about when they upgrade to lithium.
The charging profile mismatch, explained simply
Lead-acid batteries like a slow, patient charge: bulk up to around 14.4V, then a long absorption stage holding that voltage for hours, then a float stage that drops to about 13.2V to 13.6V to maintain the battery without overcharging it.
LiFePO4 batteries want something different. They charge efficiently up to roughly 14.2V to 14.6V (check your specific battery, this varies by brand), need only a short absorption period since lithium cells accept current almost until they are full, and they do not want a float stage at all. Holding a lithium battery at a float voltage for weeks on end does not damage it the way it can shorten a lead-acid battery’s life, but it also does nothing useful and some manufacturers recommend against it.
Note: This is exactly why our guide on bulk, absorption and float charging for lithium is worth reading if the terminology above is new to you.
How to check your specific converter
Find the model number on the converter’s label, usually a sticker on the side or top of the unit. It will look something like PD9160A or WF-8955-AD-MBA. Search that exact model number plus “specifications” or “manual PDF.”
Inside the spec sheet, look for the absorption voltage and float voltage numbers. Here is roughly how to read them:
- Absorption voltage 14.2V to 14.6V, float around 13.6V or lower: reasonably lithium compatible, though not perfect
- Absorption voltage 14.4V to 14.8V with a long float held above 13.8V: designed for lead-acid, will overcharge or hold lithium unnecessarily high
- A dedicated “LI” or “LITHIUM” battery type switch or dip setting on the unit: good sign, but verify the actual output voltage it produces
- Single stage constant 13.6V output with no stages at all: will undercharge most lithium banks significantly
A cheap way to verify in the real world: clamp a multimeter across your battery terminals about two hours after starting a full charge from empty on shore power. If you are not seeing at least 13.8V climbing toward 14V-plus, your converter is likely underdriving the bank.
A scenario that plays out constantly
A couple bought a 2016 Class C with a stock WFCO WF-8955 converter, no lithium switch, absorption around 14.4V but float locked at 13.6V permanently after about four hours. They installed two 100Ah Renogy lithium batteries expecting double their old capacity.
What actually happened: the converter’s absorption stage was short enough and the voltage was close enough that the batteries did charge to nearly full most of the time. The problem showed up in cold weather. Below freezing, their battery’s BMS cut charging entirely below 32°F, and the converter had no idea, so it just kept trying and doing nothing while they assumed they were topped off overnight at a ski resort parking lot.
The fix in that case was not a converter swap. It was adding a small heated battery box and confirming the low-temp cutoff on the spec sheet. Not every “converter problem” is actually the converter.
Warning: LiFePO4 batteries generally should not be charged below freezing unless they have internal heating pads. This is a battery chemistry limit, not a converter setting, and no converter upgrade fixes it. Check your battery’s low-temperature charge cutoff before blaming your converter for slow winter charging.
Converters that are known to work well with lithium
| Converter | Lithium mode | Approx. price | Notes |
|---|---|---|---|
| Progressive Dynamics PD9160ALV | Built-in Charge Wizard lithium profile | $220-$280 | Widely used direct-swap for older PD9100 series |
| WFCO WF-9800 series | Dip switch lithium setting | $200-$320 | Common OEM replacement in Forest River and Jayco units |
| Victron Orion-Tr Smart | Fully programmable via Bluetooth app | $150-$300 | DC-DC unit, good for chassis charging setups |
| Xantrex Freedom XC Pro | Selectable lithium charge algorithm | $900-$1,400 | Combined inverter-charger, bigger investment |
The common mistake: trusting the “lithium switch” blindly
A mistake I see constantly is people flipping a converter’s lithium switch and assuming the job is done. Manufacturers do not agree on what “lithium mode” means. One converter’s lithium setting outputs 14.2V, another outputs 14.6V, and a few older units labeled lithium-ready actually just disable the float stage while leaving absorption voltage untouched.
Always confirm the actual output voltage against your battery manufacturer’s recommendation. Battle Born, for instance, publishes a recommended charge voltage range on their site, and it is worth five minutes to cross-check it against your converter’s documented lithium output before calling the setup finished.
When to just replace the converter
If your converter has no lithium setting, uses a single fixed voltage under 14V, or you cannot find documentation confirming its charge profile at all, replacement is usually the cleanest path. It is typically a bolt-in swap since most RV converters share standard mounting patterns and wire gauge.
Our step-by-step converter replacement guide walks through the actual removal and wiring, and if your rig currently has a WFCO or Progressive Dynamics unit specifically, the WFCO and PD lithium-readiness guide covers model-specific quirks worth knowing before you buy a replacement.
If you are trying to figure out whether your existing charger, not just converter, is the culprit, our piece on whether a lead-acid charger can safely charge lithium is a useful next stop, especially for boat and trailer owners running separate standalone chargers rather than a built-in converter.
Checking converter compatibility takes maybe twenty minutes with a multimeter and a model number search, and it can be the difference between a lithium upgrade that actually delivers the capacity you paid for and one that quietly disappoints you every single trip. Do the check before you mount anything permanently, while you still have easy access to swap the converter if you need to.
