I got a message last fall from a guy who had just finished a lithium swap in his Class C. Two Battle Born 100Ah batteries, clean wiring, nice job overall. His question was simple: “Is it supposed to smell like a hot iron in the closet where my converter lives?” It was not supposed to do that, and it took about ten minutes on the phone to figure out why.
The quick version
- Lithium accepts much more current for much longer than lead-acid, so your converter works harder and stays hot longer than you are used to.
- Warm is normal. Too hot to touch, discolored plastic, or a burning smell is not normal and needs attention now.
- Common causes are an undersized converter, poor ventilation, a lithium profile pushing full output the whole absorption stage, or a converter never designed for lithium at all.
- Fixes range free (clear the vents) to a few hundred dollars (upgrade to a lithium-rated converter or add a dedicated charger).
- If you smell burning plastic or see scorch marks, stop using it and inspect immediately.
Why lithium makes your converter work so much harder
Lead-acid batteries taper their charge acceptance early. As a flooded or AGM battery climbs past 80 percent state of charge, internal resistance rises and the battery simply refuses to take much current. Your converter senses this and backs off, which is part of why old-school converters barely got warm.
Lithium does not play by those rules. A LiFePO4 bank will happily accept close to its full rated charge current from 20 percent all the way to nearly 95 percent state of charge. A 45-amp converter that used to spend most of its life outputting 8 to 15 amps to a lead-acid bank might now sit at 35 to 40 amps for two or three hours straight while it fills a lithium bank after a day of heavy use.
That is not a malfunction. That is the converter doing exactly what it was asked to do, just for a lot longer at a lot higher output than its designers probably tested for in the real world.
The most common causes, in order of how often I actually see them
Before you assume the worst, walk through these in order. Most cases turn out to be one of the first two.
1. Blocked or minimal ventilation
Converters are almost always mounted in a cabinet, closet, or under a dinette seat. Manufacturers assume some airflow around the case. Owners then fill that space with shoes, extra bedding, or a stack of camp chairs, and airflow drops to nothing.
2. An undersized converter for the new load
Many RVs ship with a 45 or 55-amp converter sized to trickle-charge a modest lead-acid house battery and run 12V lighting. Add a 200 to 400Ah lithium bank that wants to gulp current, and that converter is now running near its ceiling for hours at a time.
3. No lithium charge profile, or the wrong one selected
Some converters, including certain WFCO and Progressive Dynamics models, have a lithium mode that shortens absorption time and sets a proper float voltage. If that mode is not enabled, the unit can sit in a lead-acid-style absorption stage far longer than lithium needs, generating heat the whole time for no real benefit.
4. A converter that was never built for lithium at all
Older single-stage or basic multi-stage converters just push a fixed voltage and let the battery sort it out. Lithium’s flat voltage curve and huge current appetite can push these units well past their comfortable duty cycle.
Warning: a converter that smells like hot electronics, shows browned or melted plastic near the vents, or trips its internal thermal protection repeatedly is not a “let it run and see” situation. Disconnect shore power and have it inspected before you use it again.
What normal heat actually feels like
This is the part people get wrong most often, because “hot” is subjective.
| What you feel or see | What it likely means |
|---|---|
| Warm case, comfortable to rest your hand on for several seconds | Normal operation under moderate load |
| Hot case, you pull your hand back within a second or two | Working hard, borderline. Check ventilation and load. |
| Too hot to touch at all, faint plastic or electrical smell | Past safe operating range. Investigate now. |
| Internal fan (if equipped) running constantly on high | Normal on a hot day under heavy charge, worth monitoring |
| Repeated shutdowns or breaker trips | Thermal protection is doing its job. Do not ignore it. |
A real scenario worth learning from
The camper I mentioned earlier had a 45-amp WFCO converter original to a 2016 build, paired with a new 200Ah lithium bank. After a weekend of boondocking-adjacent camping with the generator, he’d plug into shore power and the converter would push near its max output for two straight hours in a closet with the door shut and a stack of blankets against the vent.
We opened the door, pulled the blankets, and the case temperature dropped noticeably within twenty minutes. That solved the smell. But the converter was still running flat out for over an hour every time, which told us it was undersized for the new bank long term. He ended up adding a dedicated Progressive Dynamics lithium-profile converter rated higher, and the original unit now just handles 12V house loads.
The common mistake to avoid
The mistake I see most is people assuming any heat means a defective unit, unplugging everything, and giving up on shore charging entirely rather than diagnosing it. The second most common mistake is the opposite: ignoring real warning signs like a burning smell because “converters always run warm.”
Both extremes cause problems. The fix is to actually check airflow, actually check the amp draw with a clamp meter if you have one, and actually confirm whether your converter has a lithium mode before assuming it needs replacing.
How to fix it, cheapest option first
- Clear anything blocking the converter’s vents or fan intake, and leave a few inches of open air around the case if the cabinet allows it.
- Check the manual or the label for a lithium/LiFePO4 charge profile switch or dip setting, and enable it if present.
- Add a small 12V computer-style fan aimed at the case if the cabinet runs warm generally, especially in summer heat.
- Use a clamp meter to see actual output current during a charge cycle, and compare it to the converter’s rated max.
- If the unit is running at or near its rated max for hours regularly, plan to upgrade to a higher-amperage, lithium-rated converter or add a dedicated lithium charger alongside it.
- If you smell burning plastic, see discoloration, or hear repeated clicking from a thermal breaker, stop use and have it inspected before your next trip.
Tip: when shopping for a replacement, look at both the continuous amp rating and whether the spec sheet explicitly lists a lithium or LiFePO4 charge profile, not just “compatible with lithium.” Brands like Progressive Dynamics and WFCO both make units with true lithium profiles built in.
If you’re not sure your current converter is even the right type for lithium in the first place, it’s worth starting with whether your RV converter is lithium compatible before you spend money on cooling fixes. And if the heat issue turns into a bigger conversation about replacing the unit entirely, our guide to replacing an RV converter for lithium walks through sizing and installation.
It also helps to understand how bulk, absorption and float charging actually work with lithium, since a converter stuck in a long absorption stage built for lead-acid is one of the sneakier reasons it overheats. For general safety limits on wiring and fusing near a hot converter, the American Boat and Yacht Council publishes standards that many RV electrical systems borrow from even though they’re written for boats.
A converter running warm after a lithium swap is not automatically bad news. It usually just means the battery is finally accepting the charge it always should have been getting, and the converter is working to keep up. Give it airflow, confirm it has a real lithium profile, and keep an eye on how long it runs at full output. If it settles into “warm but tolerable,” you’re fine. If it stays punishing to the touch trip after trip, that is your cue to size up rather than live with it.
