The battery is the cheapest part of a lithium conversion. That sentence is the whole article, and almost every quote you will read online gets it backwards.
Search “RV lithium upgrade cost” and you will find a price for two 100Ah LiFePO4 drop-ins and very little else. The implication is that a lithium retrofit is a swap: pull the old lead-acid batteries out, put the new ones in, tighten four bolts, done. On a 2004 travel trailer with a stock converter and 4 AWG battery cable, that swap will give you a bank that never charges past about 80 percent, a converter that cooks itself trying, and a battery monitor reading numbers that mean nothing.
The honest number for a competent 200Ah conversion on an older rig, done by the owner with hand tools, is $1,400 to $3,200. For 400–600Ah with an inverter and proper alternator charging, budget $3,000 to $6,500. Paid installation adds $800 to $2,500 depending on how much of the existing wiring has to be replaced.
Here is where all of that money goes, and which parts you can defensibly skip.
What actually has to change, and why
An older RV’s 12V system was designed around the electrical behaviour of flooded lead-acid. Four assumptions are baked into it, and lithium violates all four.
Lead-acid absorbs charge slowly; lithium does not. A flooded bank will accept maybe 20–25 percent of its capacity in amps before it starts gassing. LiFePO4 will accept 50 percent or more, and a 200Ah bank will happily pull 100A from anything willing to supply it. Your converter, your alternator and your battery cable were all specified against the lead-acid number.
Lead-acid wants a long absorption phase; lithium wants voltage and then nothing. A stock WFCO or Magnetek converter runs a lead-acid profile that tapers to a float of around 13.2–13.6V. LiFePO4 sits at roughly 13.3–13.4V at rest, so a lead-acid float voltage delivers almost no current. The bank stalls in the high 80s or low 90s, indefinitely, and the owner concludes lithium was oversold.
Lead-acid tolerates voltage sag; lithium exposes it. A lead-acid bank sags under load anyway, so cable losses hide inside battery behaviour. LiFePO4 holds voltage nearly flat until it is nearly empty, which means every millivolt lost in undersized cable shows up as a real, visible problem — inverters cutting out, chargers derating, monitors disagreeing with each other.
Lead-acid fails gradually; lithium fails abruptly and with more energy behind it. A 200Ah LiFePO4 bank can deliver several thousand amps into a dead short. Standard ANL fusing is not rated to interrupt that. This is the part of the job that is genuinely a safety matter rather than a performance one.
If you want the arithmetic on whether lithium earns its price at all, that belongs in the cost-per-cycle comparison between LiFePO4, AGM and flooded lead-acid rather than here. This article assumes you have already made that decision and now want to know what the invoice looks like.
The full parts list, costed
Prices are US retail as of mid-2026, in ranges, for planning only. They move constantly and the spread between budget and premium in this category is wider than in almost any other RV component class.
| Item | Budget | Mid | Premium | Skippable? |
|---|---|---|---|---|
| 2 × 100Ah LiFePO4 12V drop-in | $360 | $700 | $1,300 | No |
| Converter/charger with lithium profile (55–60A) | $230 | $330 | $480 | Rarely — see below |
| DC-DC charger (30–50A) | $150 | $260 | $420 | Only if you never charge while driving |
| Class T fuse + holder | $55 | $85 | $130 | No |
| Battery cable, lugs, heat shrink (2/0 or 4/0) | $90 | $180 | $340 | No |
| Shunt-based battery monitor | $95 | $140 | $220 | Technically yes. Don’t. |
| Busbars, MRBF/ANL branch fusing, terminal covers | $60 | $120 | $210 | No |
| Battery tray, hold-down, relocation hardware | $40 | $110 | $260 | No |
| MPPT charge controller (if adding or upgrading solar) | $110 | $260 | $520 | If no solar |
| Inverter, 2000–3000W pure sine (if adding) | $290 | $700 | $1,600 | If no 120V loads |
| Consumables: lugs, crimps, cable ties, sealant, labels | $40 | $70 | $120 | No |
| Core 200Ah conversion, no solar, no inverter | $1,080 | $1,905 | $3,360 | |
| 200Ah with solar controller and 2000W inverter | $1,480 | $2,865 | $5,480 |
Two line items in that table are the ones that get left out of every forum estimate, and they are the two that determine whether the conversion works.
The converter is not optional, and “lithium compatible” is a marketing term
The single most common failed lithium retrofit is a good battery attached to a lead-acid converter. The owner spends $700 on cells and $0 on charging, and then spends six months wondering why the bank never reads full.
You have three routes. Replace the converter with a lithium-profile unit — a 55–60A deck-mount from Progressive Dynamics, WFCO, or an equivalent — for $230–$480. Add an external multi-stage charger and leave the old converter feeding the 12V distribution panel only, which is more expensive but keeps a working backup. Or, if you have a decent MPPT controller and enough array, accept that solar does the bulk charging and shore power charging stays mediocre.
Be sceptical of “lithium compatible” on older converters. Some manufacturers mean a genuine 14.2–14.6V bulk stage with a lithium float. Others mean the unit will not immediately fail when connected to a lithium bank. Check the published charge profile voltages, not the badge. If the datasheet does not state bulk and float voltages, assume it is lead-acid.
There is one legitimate skip: if the rig lives permanently off shore power and charges entirely from solar and alternator, the converter matters much less. That is a real use case. It is not the common one.
The alternator will not charge lithium safely on its own
The factory charge line from the tow vehicle or chassis alternator — usually a relay or isolator feeding through the 7-pin connector or a chassis-run cable — was sized for a lead-acid bank that self-limits its own charge acceptance.
A lithium bank does not self-limit. It will pull whatever the alternator can produce, continuously, until it is full. On a modern alternator with no external regulation, that means running at or near full output for an hour or more with no airflow benefit from engine load. Alternators are rated for intermittent peak output, not sustained maximum. Sustained maximum is how you replace an alternator.
The fix is a DC-DC charger: $150–$420 for a 30–50A unit. It caps the current draw at a value the alternator can survive, isolates the two banks, and delivers a proper lithium charge profile instead of raw alternator voltage. On a towable, it also solves the fact that the 7-pin charge wire is typically 10 or 12 AWG over 25 feet and delivers a trickle at best — see the DC wire gauge reference tables for what that run is actually capable of.
Sizing: a 30A DC-DC is adequate for most 200Ah banks with a stock alternator. Go to 40–50A only if you have verified the alternator’s continuous rating and have upgraded the cable to suit. Bigger is not better here; bigger is a service bill.
Class T fusing, and why ANL is not enough
Every battery bank needs a main fuse as close to the positive terminal as practical. On lead-acid, an ANL fuse is fine. On lithium, it may not be.
The relevant specification is the interrupt rating — the maximum fault current the fuse can safely break without arcing across the gap. ANL fuses are commonly rated in the low thousands of amps. A 200Ah LiFePO4 bank with low internal resistance can deliver considerably more than that into a hard short. Class T fuses carry interrupt ratings in the tens of thousands of amps and are the standard recommendation for lithium house banks in marine practice.
The cost difference is roughly $50. There is no version of this trade-off that favours saving it.
Branch circuits — inverter feed, DC-DC feed, distribution panel feed — get their own fusing sized to the cable, not to the load. MRBF terminal fuses or a fused busbar handle this neatly for $60–$210 depending on how many branches you have.
Cable: the cost nobody sees coming until they measure
Most older RVs have 4 AWG or even 6 AWG between the battery and the distribution point, because a lead-acid system rarely moved more than 40–60A. Add a 2000W inverter and you are asking for roughly 200A on the DC side.
At 200A on a 10-foot one-way run, 4 AWG loses about 0.5V — over 4 percent of a 12V system, before you count terminals and the fuse. Move to 2/0 and the same run loses about 0.32V. On a 15-foot run at inverter surge currents, the difference between adequate and undersized cable is the difference between a working inverter and one that shuts down every time the microwave starts.
Budget $90–$340 for cable, lugs and heat shrink depending on run length and gauge. A proper hydraulic crimper is $50–$120 and is worth buying rather than relying on a hammer crimp; poor crimps are the most common source of heat and voltage loss in DIY installs. Full gauge selection by current and distance is in the wire gauge reference tables.
The battery monitor you were going to skip
Lithium’s flat discharge curve means voltage tells you almost nothing about state of charge. Between 90 percent and 20 percent, a LiFePO4 bank moves through roughly half a volt. Your existing four-LED panel meter is now decorative.
A shunt-based monitor — $95–$220 — counts amp-hours in and out and is the only way to know what the system is doing. It is also the only way to find out whether the retrofit actually worked. Skipping it is a false economy of the highest order: you will have spent two thousand dollars on a system you cannot measure.
The job, step by step
Working order matters. Do it in this sequence and you will not have to redo anything.
1. Audit before you buy. Measure the existing battery cable gauge and run length. Photograph the converter model plate. Find out whether your solar controller, if any, has a lithium profile. Identify where the chassis charge line lands. An hour with a torch and a notebook here saves several hundred dollars of wrong parts.
2. Calculate the bank size against real consumption, not aspiration. Most owners overbuy capacity and underbuy charging. The sizing logic — and the reason shoulder-season use changes the answer — is covered in the battery bank sizing guide.
3. Disconnect everything. Negative first, then positive. Then confirm with a meter rather than trusting the switch. Solar panels produce voltage in daylight regardless of what any switch says; cover them or disconnect at the controller.
4. Remove the old bank and clean up the compartment. Flooded lead-acid leaves sulphate deposits and corroded terminals. Neutralise with baking soda solution, rinse, dry. Inspect the tray for corrosion damage — this is when you find out the tray needs replacing.
5. Fit the tray, hold-down and battery location. LiFePO4 drop-ins are lighter than the batteries they replace, typically 26–31 lbs against 60+ lbs for a group 31 flooded battery. The old hold-down may not fit the new case dimensions. If you are relocating the bank inside, confirm the new location is not somewhere that will drop below freezing in your use pattern, because charging below 0°C damages standard LiFePO4 cells permanently unless the pack has integral heating.
6. Install the main fuse and busbars before the battery. Build the distribution side first, with everything unpowered. Fuse holder as close to the positive terminal as the layout allows — measured in inches, not feet.
7. Run the new cable. Grommet every bulkhead pass-through. Support every 18 inches. Keep positive and negative bundled together where practical. Do not run battery cable through the same hole as anything sharp, and do not rely on the existing routing being adequate — it was routed for smaller wire.
8. Replace the converter. Deck-mount converters in older rigs are usually a slide-out module in the distribution panel; the swap is typically four screws and three wires. Verify the output voltage with a meter after commissioning rather than trusting the label.
9. Install the DC-DC charger. Input from the chassis or tow vehicle side, output to the house bank, both sides fused. Mount it where it has airflow — these run hot at full output.
10. Install the shunt. It goes on the negative side, between the battery negative and every other negative in the system. Every load and every charge source must return through the shunt or the counting is wrong. This is the step people get wrong most often.
11. Commission and verify. Connect the bank. Confirm converter output voltage at the battery terminals under charge — it should reach the manufacturer’s specified bulk voltage, typically 14.2–14.6V. Confirm the DC-DC charger current with the engine running. Load-test the inverter with your largest appliance and watch battery voltage under load. Then label everything, because in two years you will not remember.
12. Tell your insurer. This is not optional paperwork. A significant electrical modification changes the risk profile of the vehicle, and an undeclared modification is a straightforward route to a denied claim after a fire. The distinction between agreed-value and actual-cash-value cover matters enormously here, and it is covered properly in the guide to insuring a custom or converted vehicle.
Where the money actually went: two worked examples
A 2007 travel trailer, 200Ah, solar already fitted, owner-installed. Two mid-tier 100Ah drop-ins ($700), 60A lithium converter ($330), 30A DC-DC charger ($260), Class T fuse and holder ($85), 25 feet of 2/0 cable with lugs ($180), SmartShunt ($140), busbar and branch fusing ($120), tray and hardware ($110), consumables ($70). Total: $1,995. Existing MPPT controller had a lithium profile and was retained. Roughly 14 hours of work over a weekend.
A 2012 Class C, 400Ah, adding a 3000W inverter, paid install. Four 100Ah drop-ins ($1,400), 60A converter ($330), 50A DC-DC ($420), 3000W inverter ($900), MPPT upgrade ($260), Class T and branch fusing ($210), 4/0 cable and lugs ($340), monitor ($140), tray, relocation and hardware ($260), consumables ($90). Parts: $4,350. Installation at an independent shop: $1,700. Total: $6,050.
The second number is the one worth sitting with. At $6,050, the conversion is a material fraction of what the rig is worth, and the question stops being technical and becomes financial — which is exactly the calculation in upgrading an older rig versus buying new. If your rig has structural issues, water ingress history, or an appliance set that is due for replacement anyway, spending six thousand dollars on its electrical system is not obviously the right move.
What we would skip, and what we would not
Skip: the second inverter, the 600Ah bank on a rig used twelve weekends a year, the premium branded cells if the mid-tier option has a real warranty and a proper BMS spec sheet, and the fancy display panel if you already have a shunt with a phone app.
Do not skip: the converter, the Class T fuse, the shunt, the cable upgrade, or the DC-DC charger if you charge while driving. Every one of those is either a safety item or the thing that makes the expensive part of the system function.
The failure mode we see repeatedly is a $900 battery purchase followed by $200 of everything else, and a system that underperforms the lead-acid setup it replaced. Charging infrastructure is not the accessory. It is the job.
Once the bank is in, the remaining question is how the three charge sources — shore, solar and alternator — coordinate without fighting each other, which is its own piece of work: see building a three-source charging system.
Frequently asked questions
Can I just drop lithium batteries in without changing anything else? Physically, yes. The system will run. It will charge slowly, never reach full capacity on shore power, and put your alternator under sustained load it was not designed for. You will have bought lithium’s weight advantage and none of its capacity or cycle-life advantage.
How long does the retrofit take? A straightforward 200Ah conversion with no cable rerouting is a solid weekend for a competent DIYer. Add an inverter, new cable runs and a converter swap and it becomes 20–30 hours. Shops typically quote 8–16 hours of labour, which assumes they are not fighting the existing wiring.
Do I need to upgrade my solar charge controller? If it has a selectable lithium or user-defined profile with adjustable absorption and float voltages, no. If it is an old PWM unit with fixed lead-acid setpoints, yes — and you should probably be upgrading it anyway for reasons that have nothing to do with the battery.
Is 200Ah of lithium equivalent to 400Ah of lead-acid? Roughly, in usable energy terms, because lead-acid should not be discharged below 50 percent while LiFePO4 tolerates 80–90 percent depth of discharge. It is not equivalent in charge acceptance, weight, or cycle life, and those differences are where the real value sits.
What happens if the batteries freeze? Standard LiFePO4 cells must not be charged below 0°C (32°F); doing so causes lithium plating and permanent capacity loss. Most quality drop-ins have BMS low-temperature charge cutoff that prevents this automatically. Discharging at low temperature is generally fine, with reduced capacity. If the bank lives in an unheated exterior compartment and you camp in winter, buy self-heating cells or plan the install around an interior location.
Can I mix lithium and lead-acid batteries in the same bank? No. Different charge profiles, different internal resistance, different voltage curves. In parallel, the lithium bank will source current into the lead-acid bank and neither will be charged correctly. Separate banks with a DC-DC charger between them is the only sane arrangement.