Boondocking the Arizona Desert: Sizing the House Battery and Solar You Actually Need

Every fall, a few thousand rigs point south toward Quartzsite, the La Posa long-term areas, and the BLM ground around Yuma — and a good share of them arrive with a power system somebody sold them at an RV show. If you're buying or upgrading before this winter, the useful question isn't "how many watts of solar should I get." It's "how many amp-hours do I burn between sunsets, and what does January sun actually give back?" Answer those two and the shopping list writes itself. Here's the math, in the numbers a desert winter actually produces.

Start with a load budget, not a battery brochure

Add up what you use in 24 hours, in amp-hours at 12 volts. Amps × hours. Real numbers from typical rigs:

• Furnace blower — 7 to 9 amps while running. This is the one that ruins budgets. Quartzsite nights in January drop into the 30s, and a furnace cycling through a cold night easily eats 25–35 Ah on its own.
• Absorption fridge on propane — 0.3 to 0.6 A continuously for the control board and igniter, so 8–15 Ah a day. A 12V compressor fridge is a different animal: 30–60 Ah a day, more when the rig is hot.
• Water pump — 5–8 A, but only while it runs. Call it 3–6 Ah a day for two people being careful.
• LED lights — 1–2 A total for a whole rig lit up. Rounding error.
• CPAP — 4–5 Ah a night without the humidifier, 15–20 Ah with it. Turn the humidifier off; the desert will thank you.
• Phones, laptops, Starlink, the TV — 10–40 Ah depending on how much you work from the rig.

A conservative couple in a travel trailer lands around 50–80 Ah a day in cool weather. Add a residential fridge, a work laptop, and a satellite dish and you're at 120–180 Ah. Write your number down. Everything below is sized off it.

What "200 amp-hours" actually buys you

Nameplate capacity and usable capacity are not the same number, and that gap is where most disappointment lives.

Flooded or AGM lead-acid gives you about half its rating before you start shortening its life — a 200 Ah AGM bank is roughly 100 Ah of real budget. Pull it hard and Peukert's effect takes another bite, so a high-draw night gives you less than the meter promised. Voltage sags as it discharges, which is why your lights dim and the inverter starts complaining at 40%. A group 31 AGM runs $200–$320 and weighs 65–75 pounds.

LiFePO4 gives you 80–100% of its rating, holds voltage nearly flat until it's nearly empty, and takes a charge four to five times faster — which matters enormously when you only get six good solar hours in December. A 100 Ah lithium is $250–$500 and weighs about 26 pounds. Two of those replace four golf-cart batteries and save 150 pounds of tongue weight.

Two lithium cautions that catch desert snowbirds specifically. First, do not charge LiFePO4 below freezing — 20-degree mornings in Quartzsite are normal, and charging a cold cell permanently plates it. Buy a battery with a built-in heater or low-temp cutoff, not the cheapest drop-in. Second, your converter probably has the wrong profile. Plenty of factory WFCO and Progressive Dynamics units float at 13.6 V, which leaves lithium at roughly 85% forever. If you go lithium, budget for a lithium-capable converter or a DC-DC charger too.

Size solar for December sun, not June sun

A 100-watt panel does not make 100 watts. Flat-mounted on an RV roof in Arizona in January, with the sun topping out near 33 degrees above the horizon, expect 25–35 Ah per 100 watts per day. Summer is better in raw hours but panels lose 10–15% of their output to heat, so the practical planning number doesn't move as much as you'd hope.

Run it against your load budget:

• 200 W → 50–70 Ah/day. Fine for a fridge-on-propane, no-furnace, weekend rig.
• 400 W → 100–140 Ah/day. The sweet spot for most full-timers.
• 600–800 W → 150–280 Ah/day. Residential fridge, real work-from-the-rig loads.

Two hardware notes worth the money. MPPT beats PWM by 20–30% in cold, low, winter light and lets you wire panels in series so thinner wire carries the power. And check the wire before you add panels: most factory "solar prep" ports are 10 AWG, which realistically caps you around 400 watts at 12 volts. Going bigger means pulling new cable, not just bolting on glass.

The inverter, the alternator, and the parts nobody budgets

An inverter is where amp-hour math gets violent. A 1,000-watt microwave pulls about 100 amps from a 12 V bank while it runs; a drip coffee maker is similar. That's survivable for four minutes and ruinous for forty. Running a rooftop air conditioner off an inverter is a real project — a 13,500 BTU unit surges near 3,000 watts and needs a soft-start plus a large lithium bank to be anything but a party trick.

Wiring is the part that gets skipped and the part that starts fires. A 2,000-watt inverter needs 2/0 or 4/0 cable and a Class-T or ANL fuse within 18 inches of the battery positive. If a quote for an inverter install doesn't mention the fuse, get a different quote.

Finally, charging while you drive: if you've gone lithium, don't wire the battery straight to the tow vehicle's charge line. Lithium will accept everything an alternator can give and cook it. A 30–60 amp DC-DC charger ($180–$350) limits the draw and gives you the correct charge profile — and on a cloudy week in the desert, a two-hour drive to town for water becomes real charging.

When to call a pro

Some of this is genuinely DIY. Some of it isn't, and the line is about consequences: a mistake in 120-volt or high-current DC wiring burns the rig down, and a bad ground makes you chase ghosts for a season.

Call a mobile tech when the batteries won't hold overnight and you've already ruled out the obvious drains, when the converter isn't bringing the bank up on shore power, when you want an inverter, DC-DC charger, or new roof array installed and fused correctly, or when there's any smell of hot plastic, any warm terminal, or any corroded cable end. If the whole 12-volt side has gone dark rather than weak, that's a different diagnosis — start with tracing it from the battery to the fuse panel before you buy anything.

Winter in the desert is exactly when a dead bank is hardest to fix yourself. A vetted, licensed, insured mobile tech can come to your site — that's what RV electrical repair in Yuma means in practice, and the same goes for anywhere in Phoenix or the rest of the areas we cover.

FAQ

How much solar do I need to run my air conditioner? More than fits on your roof, in most cases. An AC pulling 1,400 running watts for eight hours is roughly 900 Ah at 12 volts — several thousand watts of panel and a very large lithium bank. Plan on a generator or shore power for AC and size solar for everything else.

Is lithium worth it if I only camp a few weeks a year? Often not. If you're mostly on shore power and take two trips a year, a good pair of AGMs and 200 watts of solar is the better value. Lithium earns its price when you cycle it hard and often.

Can I mix a new battery with my old one? No. Two batteries wired together age to the weakest one, and you cannot mix lithium with lead-acid on the same bus at all. Replace the bank as a set.

What do I do if my bank dies mid-trip? Call 833-FIXED-RV (1-833-349-3378). One call, answered live 24/7, and we connect you with a vetted local pro who comes to your site — free for you to use, and the work is backed by our $2,500 Workmanship Guarantee.