Most camper vans need 200 to 400 amp hours of lithium storage and 200 to 600 watts of solar, and almost every van that gets this wrong gets it wrong in the same direction: too much battery, not enough charging. The number that decides both is your own daily draw. Work that out first and the rest of the specification stops being a guess.
The short answer
- A two-person van without air conditioning draws 60 to 100 amp hours a day, which sizes to 200 to 300 amp hours of lithium and 400 to 600 watts of solar.
- A 50 amp charger from the alternator returns 50 amp hours for every hour of driving, against about 87 from a 350 watt array on a perfect summer day.
- A fitted 300 amp hour system with 600 watts of solar runs $10,050 to $20,710 at an American shop, and 40 to 70 hours of that is labour.
- A complete lithium system weighs 230 to 340 pounds, which is 7 to 10 percent of the payload Mercedes publishes for a Sprinter 2500 on the 170 inch high roof.
- Running a 12 volt air conditioner overnight costs 150 to 250 amp hours, more than everything else in a normal van combined.
What most camper vans actually need
The short answer for two people living in a van year round without air conditioning is 200 to 300 amp hours of lithium at 12 volts, 400 to 600 watts of roof solar, and a 30 to 50 amp charger pulling power off the alternator while you drive. That combination carries a fridge, lights, a roof fan, a diesel heater, a water pump and the usual pile of devices, with 2 days of slack for a stretch of cloud. A weekend van in summer needs half of it. A van running air conditioning overnight needs 3 times it, and pays for that in weight before it pays for it in money.
The answer arrives as a band rather than a number because two vans with identical cabinets can draw twice as much as each other. A fridge in Arizona in July works a great deal harder than the same fridge in Oregon in October. Somebody working from the van with a satellite terminal up 10 hours a day is carrying a load that barely existed in this category three years ago. The specification follows the use, and the use is yours to state before anybody quotes you a tier.
| How the van gets used | Daily draw | Lithium bank | Solar | What actually charges it |
|---|---|---|---|---|
| Weekends in summer, fridge and lights | 30 to 50 Ah | 100 Ah | 200 to 300 W | Solar, with shore power at home between trips |
| Full time, two people, no air conditioning | 60 to 100 Ah | 200 to 300 Ah | 400 to 600 W | Alternator first, solar second |
| Winter, working from the van, satellite internet | 100 to 160 Ah | 400 Ah | 600 to 800 W | Alternator, because December solar is thin |
| A 12 volt air conditioner running overnight | 250 to 400 Ah | 600 Ah or more | 800 W and up | Alternator and shore power, not solar |
The last row is the honest one. A 12 volt rooftop air conditioner takes 150 to 250 amp hours to get through a warm night, which is more than the rest of a normal van's daily total put together. It is buildable, several shops on our rankings build it, and it costs battery, roof space, weight and money in that order. For most buyers, shade, insulation and a good roof fan get closer to comfortable for a fraction of the outlay, and that arithmetic is the case for a fan over air conditioning in any van that is not parked in Phoenix in August.
Start with the daily draw, not a package tier
Shops sell electrical in tiers because tiers are easy to quote, and a tier is a guess about somebody else's life. The alternative takes twenty minutes. List what you will run, put an amp figure and an hours figure against each one, and add it up. The result is your daily draw in amp hours at 12 volts, and every other number in the system falls out of it: the bank, the array, the controller, the charger and, in the end, the price.
Two conventions make the sum easier. Everything converts to amp hours at 12 volts, including the things that run through the inverter, because that is the unit the battery is sold in. And appliances get a duty cycle rather than a run time. A compressor fridge does not draw current for 24 hours, it draws current for the third of the day its compressor is actually running, and the difference between those two readings is the difference between a 200 amp hour bank and a 600 amp hour one.
What each thing on the list actually takes
These are working bands rather than product specifications, and they are wide because climate and habit move them further than brand does. Use them to find the shape of your own number, then replace each row with the figure on the appliance you actually buy.
| Load | Amp hours a day at 12 volts | What moves it |
|---|---|---|
| 12 volt compressor fridge | 18 to 35 | Ambient temperature and how often the door opens |
| Roof fan | 2 to 20 | Speed setting and hours, a 10 to 1 spread on its own |
| Diesel air heater | 15 to 29 | Hours of running, set by insulation more than by weather |
| LED lighting | 2 to 6 | Season, because winter evenings start at five |
| Water pump | 1 to 3 | Whether there is a shower on the system |
| Phones, laptop and camera batteries | 10 to 25 | Whether they charge through the inverter or off 12 volts |
| Satellite internet terminal | 30 to 70 | Which dish, and how many hours it stays up |
| Induction hob | 30 to 60 | How many meals get cooked on it rather than on gas |
| 12 volt rooftop air conditioner | 150 to 250 | One warm night, which beats everything above it combined |
The heater row is the only figure here taken from a manufacturer rather than from practice. Webasto publishes the Air Top 2000 STC at 1.25 to 2.45 amps in operation, which across a 12 hour night comes to 15 to 29 amp hours. That is a small number for the amount of comfort it buys, and it is the strongest argument in the van for burning diesel rather than electricity to make heat. Every electric heating answer costs many times as much out of the same bank.
One more distinction is worth drawing before the sum. A load that runs natively on 12 volts costs you what it says on the label. A load that runs through the inverter costs you that plus the inverter's own overhead, and an inverter left switched on all day draws current whether anything is plugged into it or not. Vans wired so that the fridge, the lights, the fan and the pump never touch the inverter are the ones that quietly come in under their sizing, and it costs nothing at drawing stage to build one.
Add your own list up and most people land between 60 and 100 amp hours a day for two people without air conditioning. Under 40 means a weekend van. Over 140 means air conditioning, an induction hob, or a working setup with screens and a dish running most of the day. Whichever number it is, it is now the only input the rest of this post needs.
Summer and winter are two different vans
The load does not shrink in winter, it moves. The fridge works less, the heater works more, the lights are on longer because it is dark at five, and the array that carried you through July returns a fraction of it in December. Two of those three changes push the same direction while the third is the only one helping, which is why a system sized on a good summer week is the system that runs out in January.
Winter draw is mostly the heater, and insulation decides how often it cycles, which makes it an electrical decision as much as a comfort one. A van that holds heat asks the heater for 6 hours of running a night. A van that does not asks for 12, and pays for the difference twice, once in amp hours and once in diesel. That is the cheapest 15 amp hours a day anyone will ever save you, and it is only available while the walls are still open.
From the desk
Storage gets quoted in two different units and the bigger-sounding one usually lands on the brochure. A 300 amp hour bank at 12 volts is 3.6 kilowatt hours, so a 15 kilowatt hour system is a bit over 4 times it rather than 50 times it. Ask every shop for amp hours, the nominal voltage and the usable percentage in the same sentence. Two quotes that looked incomparable turn out to be 280 usable amp hours against 320, and the conversation moves on to charging, which is where it should have started.
Sizing the battery bank
Storage is daily draw times the number of days you want to survive without a charging source, divided by the fraction of the bank you are allowed to use. The first two terms are yours. The third is chemistry, and it is where most of the confusion in this category lives.
Lithium or AGM, and why the answer is nearly always lithium
Lithium iron phosphate is usable to about 80 percent of its rated capacity. AGM lead acid is usable to about 50 percent if you want it to reach its rated life. The consequence is arithmetic rather than opinion. Matching 400 usable amp hours of lithium takes roughly 640 amp hours of AGM, which means a bigger box, a heavier van and more frequent replacement in exchange for a lower price on the day.
AGM still has a case, and it is a narrow one. A van used 4 weekends a year, stored on shore power, whose bank never sees a deep discharge, does not need lithium and will not notice the difference. Everything else does. The purchase price gap has closed far enough over the last few years that the weight argument now decides it on its own, before anyone gets as far as cycle life.
How many days of autonomy to build for
2 days is the sane default for a van that drives most days, 3 for a van that gets parked for a week at a time, and 4 is a specification a lot of people talk themselves into and never use. Each extra day is capacity you carry every mile whether or not you ever spend it, and it is the easiest place in the whole build to buy weight you do not need.
Worked on an 80 amp hour daily draw: 2 days is 160 usable amp hours, which is a 200 amp hour lithium bank. 3 days is 240 usable, so 300 amp hours. 4 days is 320 usable, so 400 amp hours and about 110 pounds of batteries before a single other component in the system is counted. Written out like that, the third day is cheap and the fourth day is a decision.
The inverter puts a floor under all of it. A 1,000 watt inverter working flat out asks the bank for roughly 85 amps, so 100 amp hours is the practical minimum behind it and 200 is the comfortable one. A 2,000 watt inverter wants 200 amp hours as a minimum and closer to 300 once a real buffer is included. Specifying an inverter big enough for an induction hob and then fitting one battery behind it is the most common way to end up with a system that trips under load and a shop that cannot explain why.
Costs money to get wrong
Lithium will not charge below freezing
Lithium iron phosphate cells take permanent damage if they are charged below 32 degrees, and a van parked at 8,000 feet in March gets there overnight without anybody noticing. The fix is a bank with internal heating, or a battery box inside the insulated envelope with a low temperature cutoff wired into the charge controller, and it costs $200 to $900 depending on which route the shop takes. The expensive version is a $3,000 bank replaced in its second winter because it was mounted in an unheated garage under the bed, where it was easy to reach and nobody asked what the temperature was.
Wiring, fusing and the parts nobody photographs
The battery is the cheapest thing in the system to change later and the cable is the most expensive. Conductor size is set by current and run length, so a van wired for 200 amp hours cannot simply be handed another 200 amp hours in year three. The same goes for the fuse block, the bus bars and the main disconnect. None of it appears in a photograph and all of it decides whether the system can grow at all.
A battery monitor with a shunt is the addition almost every owner wishes had been fitted on day one. Voltage on its own is a poor guess at state of charge on lithium, which sits at close to the same voltage across most of its usable range. A shunt counts amp hours in and out and turns the bank from a guess into a reading, for a couple of hundred dollars fitted. Without one, the honest answer to how much charge is left is that nobody in the van knows.
Ask where the fuses live and how you reach them. A system whose main fuse hides behind a screwed panel under a bed platform is a system you will never check, and the first time you have to it will be dark, raining, and 40 miles from anywhere with a socket set.
Sizing the solar array
The rule of thumb that survives contact with reality is that every 4 watts of panel returns about 1 amp hour a day, averaged across a year. An 80 amp hour daily draw therefore points at roughly 320 watts, and most shops round that up to 400. The rule is pessimistic in June and generous in December, which is the entire point of using an annual average rather than a best case.
Roof area is the real ceiling and it was set the day the chassis was chosen. Once a roof fan, a vent and any skylight have taken their share, most shops get 300 to 400 watts onto a 144 inch roof and 600 to 800 onto a 170. That makes choosing between Sprinter, Transit and ProMaster a solar decision as much as a driving one, and it is not a decision you recover later without pulling panels off to fit differently shaped ones.
The charge controller is sized to the array rather than to the battery, and it should be MPPT rather than PWM on anything above about 200 watts. A controller rated below the array clips output on exactly the bright cold days when the array is producing most, which is the worst possible day to throw power away. It is a $280 to $650 component doing a job no amount of extra battery can compensate for.
Panel choice matters less than mounting. Rigid panels on a proper rack outlast flexible panels glued to a roof by a wide margin, and they run cooler because air moves underneath them, which is worth real output on a hot day. Flexible panels earn their place on a pop top or a curved roof where nothing else fits, and nowhere else. Whichever goes on, ask how the mounts penetrate the roof and what seals them, because that is where a solar array turns into a leak.
Shading behaves worse than people expect. A single branch across one corner of a series-wired array can drag the whole string down, which is why arrays that live under trees get wired in parallel or split across two controllers. It costs a little more in cable and controller, and it is the difference between a bad day and a useless one.
Solar is not the main charging source
A 350 watt array on a genuinely good summer day returns something like 87 amp hours. A 50 amp DC to DC charger returns 50 amp hours for every hour the engine runs. One hour of driving is therefore worth well over half a perfect solar day, and most vans drive most days. Sized honestly, the alternator is the primary charging source in the majority of American builds and the roof is the backup.
The wrong version of alternator charging is a bare relay tying the two batteries together. Vans with smart alternators vary their output by design, and a lithium bank will pull whatever current is offered until something gets hot. A DC to DC charger sits between the two and limits current to a figure the alternator, the cable and the battery can all live with. That is the reason it costs more than a relay, and it is not a place to save $300.
What the charger can deliver depends on the alternator the van was built with, which changes by platform and by option box. Ford Pro lists the Transit's cargo configurations, and a shop should be able to tell you which alternator is in the van it is quoting on before it specifies a charger against it. A 50 amp charger behind an alternator with nothing left to give is a component that cost you money and returns you 20 amps.
Shore power is the third source and the least interesting until the week you need it. A 50 amp shore charger refills a 300 amp hour bank in around 6 hours from half empty. What matters is that it exists and is wired to a proper external inlet, because the alternative is a van that has to be driven to be charged and cannot be left plugged in on a friend's driveway for a weekend.
A generator is the fourth answer and it is usually the wrong one. It solves the same problem as an alternator charger, at the cost of fuel, noise, weight and a permanent place to store a fuel can, on a vehicle that already carries an engine and an alternator capable of doing the job while you drive to the trailhead.
A 300 amp hour system with 600 watts of solar, fitted
Total$10,050 to $20,710
Labour is the line that moves and the line almost nobody itemises. The two things that push a quote past the top of that range are a walkable solar deck and running the whole van through a 120 volt distribution panel rather than a single inverter outlet.
What the system weighs, and what that costs you in payload
Nobody enjoys this section and it is the one that changes builds. Mercedes publishes the Sprinter Cargo Van at 3,450 to 3,814 pounds of payload for the 2500 on the 170 inch high roof, which is the most common camper conversion platform in the country. Everything the shop puts in the van comes out of that number, and so do you, your passenger, your water, your gear and your dog.
| Component | Weight fitted |
|---|---|
| 400 amp hour lithium bank, four 100 amp hour batteries | 100 to 120 lb |
| The same usable capacity in AGM, about 640 amp hours | 380 to 450 lb |
| 600 watts of rigid roof panels with racks and cable | 90 to 150 lb |
| Inverter, chargers, fusing, bus bars and cable | 40 to 70 lb |
| Complete lithium system | 230 to 340 lb |
| Complete AGM system, same usable capacity | 510 to 670 lb |
A lithium system at 230 to 340 pounds is 7 to 10 percent of that published payload, which is a reasonable share for the system that makes the van habitable. The same capacity in AGM is 510 to 670 pounds, which is not. Every pound in the electrical system is a pound unavailable somewhere else, and payload is the constraint that decides the build a good deal more often than the budget is.
The other heavy system is water, and a full fresh tank outweighs the battery bank on almost every build, which is why the two get sized in the same conversation or not at all. Off Highway Van builds in aerospace aluminium rather than timber for exactly this reason, cutting several hundred pounds out of the conversion so that the payload goes to water, batteries and all-terrain suspension instead of to cabinet carcasses.
There are two ways out when the numbers do not fit, and both cost money. Take weight out of the build, which is what aluminium construction buys. Or buy more payload: Mercedes publishes the 4500 on the same 170 inch high roof at 6,382 pounds, nearly double the 2500, which is why heavy four-season builds end up on it. The first route costs money at build and the second costs money at purchase, and both are a great deal cheaper than finding the problem at a weighbridge with a finished van.
What professional shops actually fit at each price band
Sizing in the abstract is the easy half. The question underneath most of these searches is what a given budget buys from a shop that hands you a finished van, and that is answerable, because a good number of American builders publish their prices and their specifications.
| Conversion budget | What the electrical spec looks like | Shops publishing at this level |
|---|---|---|
| Systems work only | A bank, a charger and a heater fitted into a van you already own | Blue Ridge Adventure Vehicles from $5,000, Contravans on partial work |
| Under $30,000 | Lights, a fan, a fridge and a bank that will not run an inverter hard | Custom Coach Creations from $18,695, Colorado Camper Van pop-top from $15,984 |
| $30,000 to $65,000 | 200 to 300 Ah lithium, 300 to 600 W solar, alternator charging as standard | Glampervan $30,000 to $65,000, Vertical Vans $35,000 to $95,000 |
| $85,000 to $140,000 | 400 Ah or more, 600 W and up, systems sized to a climate | Papago Vans $85,000 to $140,000, DM Vans $97,000 to $105,000 |
| $120,000 and above | High-capacity four-season systems, or 15 kWh under a walkable solar deck | Vanna Adventure Vans $120,000 to $240,000, Off Highway Van $165,000 to $245,000, Brooklyn Campervans from $92,000 |
Below about $30,000 the electrical answer is a small one honestly delivered. Custom Coach Creations does full conversions from $18,695. Colorado Camper Van sells a pop-top from $15,984 and a Base Camp interior from $26,760 as two separate purchases, which is a sane way to buy at this price. What that money fits is lights, a fan, a fridge and a phone. The trap at this end is not workmanship, it is buying a van whose cable, fusing and controller were sized for the system it has rather than the system it will need in three years.
Between $30,000 and $65,000 the system becomes a real one. Glampervan works on nothing but the 136 inch high roof ProMaster in that band, and single-chassis discipline shows up in electrical more than anywhere else in a van: the same cable runs, the same panel layout and the same battery box every time, instead of a design adapted across three platforms. Vertical Vans runs $35,000 to $95,000 out of Salt Lake City on an 8 to 10 week turnaround.
Above $85,000 the specification starts answering a climate rather than a checklist. Papago Vans in Phoenix runs $85,000 to $140,000 and moves cooling load, insulation strategy and battery capacity together, because the design brief starts at 110 degrees rather than 40. Vanna Adventure Vans builds four-season rigs with high-capacity power systems in West Fargo, North Dakota, where the shop lives through the winters it specifies for. Those are two different electrical systems and both of them are correct.
At the top the numbers stop looking like a van's. Brooklyn Campervans starts conversions at $92,000 and delivers the Elevate v4 at $292,000, with a 15 kilowatt hour EcoFlow bank sitting under a walkable solar deck. Converted into the unit everybody else quotes in, that is a bit over 4 times a 300 amp hour bank at 12 volts, and it is the specification that makes air conditioning, an induction hob and a working week off-grid all true at the same time.
The step between the third and fourth rows costs the most and delivers the most, because it is where the system stops being sized to a package and starts being sized to a brief. Shops split fairly cleanly on that line, and the American builders ranked side by side show the electrical spec climbing in steps rather than smoothly as the budget rises.
The retrofit route, which almost nobody quotes
The cheapest path to a good electrical system is often not a whole van. Blue Ridge Adventure Vehicles takes work from $5,000, which at that end means systems rather than a conversion: electrical, insulation, a bed platform, a heater fitted properly. Contravans will add electrical, storage or a heater to a van somebody else already started, and turns modular work around in 4 to 6 days. Neither route shows up on a price list of finished builds, and for a reader who owns a van and has a problem it is the whole answer.
Adding capacity to a van that is already finished
Total$5,250 to $10,900
Retrofitting is not double the price of doing it once, it is roughly triple the labour, because half the job is taking apart an interior that is only in the way. The exception is the DC to DC charger, which is usually reachable from the engine bay and is the best value upgrade available on a finished van.
Where the electrical money lands in the build
Electrical is the largest single line in most professional conversions, and on a $65,000 mid-range conversion it is routinely $9,000 to $15,000 of the total. It is also the first line a cheap quote cuts, because a battery is invisible in photographs and a walnut worktop is not. Anything added after handover is money spent outside whatever you borrowed, and the loan is written against the van at handover rather than against what you bolt to it in year two.
The specification also reaches into the drawing and into the calendar. A 400 amp hour bank and a 2,000 watt inverter need somewhere ventilated, reachable and inside the heated envelope to live, and where the battery box sits in the layout gets decided at drawing stage rather than at wiring stage. High-capacity systems add shop time as well as parts cost, and the weeks a van spends on the floor move with the electrical spec further than they move with the joinery.
What to settle before you sign
Three quotes describing the same system in three different units are not three quotes. Ask everybody for the same seven things and the comparison does itself in an afternoon rather than a fortnight. A shop that hands over a labelled wiring diagram at collection has already answered half of the questions worth asking before a deposit, without anybody having to ask them.
Seven things to pin down before you sign an electrical spec
- Usable amp hours at 12 volts, not nominal kilowatt hours
- Every charging source fitted, with its amperage: solar, alternator and shore
- Where the bank sits, and whether that space stays above freezing in February
- The finished weight of the electrical system in pounds, and the payload left after it
- Which loads the inverter is sized to run at the same time
- Whether the cable, fusing and controller are sized for a later upgrade
- Who does the wiring, and whether a labelled diagram comes with the van
The system that gets built badly is almost never the one that was too small. It is the one that was sized to a brochure, wired by somebody who left no diagram behind, and mounted where the cold gets to it in February. None of those three costs anything to avoid at the drawing stage, all three cost thousands to fix afterwards, and every one of them is visible in an answer long before it is visible in a van.
