How Long Will an RV Battery Last Boondocking? One Cold Night, or Two

The furnace burns propane, but your battery pays for the 12-volt fan that pushes the heat through the ducts. As of 2026, on a freezing night the blower is estimated to use roughly 35 to 56 Ah, about as much as the other 12 V loads combined. So a 200 Ah lead-acid bank that looks big on the label hits its safe limit before the second sunset.

How long will a 200 Ah RV battery bank last boondocking?

One formula does the job: nights = usable Ah ÷ Ah used per day.

The label number tells you little. Think of the bank as a water tank with a line drawn partway down. You can draw from the part above the line. The part below is reserve, and draining it costs you battery life.

As of 2026, a 200 Ah lead-acid or AGM bank gives an estimated 100 Ah usable, with 100 Ah held back. As of 2026, a 200 Ah LiFePO4 bank gives an estimated 160 to 200 Ah usable.

Five things drain the tank every day: the furnace blower, the fridge, the water pump, the lights and the parasitic draw that never switches off. In the cold-weather example further down, a family of four uses 81 Ah a day. That works out to 100 ÷ 81 = 1.2 nights on lead-acid and 180 ÷ 81 = 2.2 nights on lithium.

How much of a lead-acid or lithium battery can you actually use?

As of 2026, a lead-acid battery routinely drained to 20 percent may wear out in a few hundred cycles, as an estimate. As of 2026, the common rule of thumb for flooded and AGM batteries is to stop at about 50 percent depth of discharge. Going deeper won't destroy the battery that night. It shortens its life every time you do it.

LiFePO4 plays by different rules. As of 2026, LiFePO4 makers typically allow use of about 80 to 100 percent of the rating, with rated cycle life of roughly 3,000 to 5,000 cycles. As of 2026, lead-acid batteries are typically rated for roughly 300 to 1,000 cycles at 50 percent depth of discharge.

Lithium has one real weakness in winter. As of 2026, most LiFePO4 manufacturers specify not charging below about 32°F (0°C), because cold charging can plate lithium and cause damage. As of 2026, many LiFePO4 spec sheets list discharge down to about -4°F (-20°C). If you camp in freezing weather and charge from solar on frosty mornings, buy a battery with built-in heaters or mount the bank inside the heated space.

Our take: if you boondock in the cold with a furnace, lead-acid is a trap. As of 2026, lead-acid costs less up front, but only about half the label is usable, and charging slows past roughly 80 percent. Say you pay $650 for 200 Ah of AGM that lasts 700 cycles. That's about $0.93 per cycle for 100 usable Ah. A $1,000 LiFePO4 bank that lasts 4,000 cycles comes to about $0.25 per cycle for 180 usable Ah. AGM still makes sense in one case: you camp a few weekends a year and the battery will age out before it cycles out.

Next question: where does the energy actually go?

What drains an RV battery the fastest?

The biggest draws in an RV are the 120-volt appliances you run through an inverter. A 1,000 W microwave pulls well over 100 A from a 12 V bank. As of 2026, an idle inverter typically draws an estimated 0.5 to 2 A, or about 12 to 48 Ah a day. A 50 W TV running through the inverter costs about 5 A.

Among the native 12-volt loads, the furnace blower is the heaviest by a wide margin. The table below shows typical draws. Multiply the amps by the hours each load actually runs.

How many amp-hours does an RV furnace use in cold weather?

As of 2026, RV ducted furnaces typically draw an estimated 3 to 8 A for the blower, depending on size and model. Larger and older units sit at the high end. The control board and igniter add a little, but the fan is where the amps go.

As of 2026, on a night near freezing a furnace is estimated to run roughly 30 to 50 percent of the time, depending on insulation and wind. Over a cold stretch of about 16 hours from evening to morning, that is 5 to 8 hours of blower time:

• 7 A × 5 hours = 35 Ah
• 7 A × 6 hours = 42 Ah
• 7 A × 8 hours = 56 Ah

If the daytime high stays below freezing too, the furnace is estimated to run roughly 30 to 50 percent of the time around the clock, as of 2026. That is an estimated 7 to 12 hours of blower time in 24 hours, or about 49 to 84 Ah at 7 A, as of 2026. A single 200 Ah lead-acid bank, usable to about 50 percent, is likely to struggle to last a full day.

Wind, single-pane windows and a 70°F thermostat setting all push you toward the high end.

These cut furnace amp-hours:

• Set the thermostat to 58 to 62°F at night and use warmer sleeping bags.
• Close the heat registers in empty rooms, such as the bathroom and the garage.
• Put reflective insulation in the windows and roof vents.

What do the fridge and parasitic draws cost your battery?

An absorption fridge running on propane is close to free for your battery. As of 2026, an absorption fridge's control board is estimated to draw about 0.3 to 0.5 A, or 7 to 12 Ah a day. The trap is its 12 V heating element. As of 2026, an absorption fridge in DC mode is estimated to pull roughly 15 to 25 A and is intended for use while driving.

As of 2026, a 12 V compressor fridge is estimated to draw 3 to 5 A while running, averaging roughly 30 to 50 Ah a day. In summer heat it uses more. That's three to five times the absorption fridge's draw, which is why a compressor fridge needs solar.

Then there's the parasitic draw that never switches off: the LP/CO detector, stereo memory, control boards and the clock on the microwave. It sounds small. As of 2026, with parasitic draw plus self-discharge, an unplugged lead-acid bank in storage may fall below 50 percent in roughly 4 to 6 weeks, as an estimate. Turn off the battery disconnect switch when the RV is parked, or keep it on a maintainer.

What does a family of four use per day, and how does a 3-night trip play out?

Picture a family of four in a 26-foot travel trailer on a national forest road in late October. Overnight lows are around 25°F. You have an absorption fridge on propane, LED lights, no solar and no generator. One day's loads, as amps × hours = Ah:

• Furnace blower: 7 A × 6 h = 42 Ah
• Absorption fridge controls: 0.4 A × 24 h ≈ 10 Ah
• Vent fan to clear condensation: 2 A × 4 h = 8 Ah
• Four phones charging: 4 A × 2 h = 8 Ah
• LED lights: 1.5 A × 5 h = 7.5 Ah
• Water pump: 6 A × 0.5 h = 3 Ah
• LP/CO detector and other parasitics: 0.1 A × 24 h = 2.4 Ah

Total: about 81 Ah a day. The furnace alone is 52 percent of it.

On 200 Ah lead-acid (100 Ah usable):

• After night 1: 81 Ah used, 19 Ah of usable capacity left. The whole bank is at about 60 percent and rests near 12.25 V.
• During day 2: you reach the 50 percent cutoff at about 12.2 V before dinner. If you keep running the furnace, by morning the bank is around 20 percent and below 12.0 V, which is the deep discharge that kills lead-acid.

On 200 Ah LiFePO4 (180 Ah usable at 90 percent):

• After night 1: 99 Ah left.
• After night 2: 18 Ah left, about 10 percent of usable capacity.
• Night 3: you need to recharge first, or the BMS shuts the bank off partway through the night.

To work out your own day, tick each load you run and add up its Ah:

• Furnace: blower amps × hours of run time As of 2026, a fridge is estimated at about 10 Ah a day on propane and 30 to 50 Ah for a compressor fridge.
• Lights: amps per fixture × fixtures × hours
• Vent fan: amps × hours
• Phones, tablets, laptops: about 1 A per phone × hours
• Water pump: amps × minutes ÷ 60 As of 2026, parasitic loads are estimated at about 0.5 to 2.4 Ah a day.
• Inverter: idle amps × 24 if it stays on, plus anything you power through it

What voltage means my RV battery is getting low?

Lead-acid voltage tracks its state of charge well, as long as you read it at rest. With the furnace running, the reading sits lower than the true charge. Switch off the loads and wait at least 30 minutes, ideally longer. As of 2026, a common stop line for flooded and AGM banks is about 12.2 V at rest.

Lithium is harder to read from voltage. As of 2026, a 12 V LiFePO4 battery typically sits around 13.0 to 13.3 V across most of its range, then drops sharply near 10 to 20 percent remaining. A voltmeter barely moves until you're almost empty.

How much solar or generator time refills the bank each day, and does shore power charge it?

Yes, shore power charges the house battery through the RV's converter. As of 2026, many older stock RV converters hold roughly 13.5 to 13.6 V. As of 2026, LiFePO4 batteries typically need about 14.2 to 14.6 V to charge fully, which older converters do not deliver. Before you switch to LiFePO4, check that your converter, solar controller and any battery charger all have a lithium profile.

As of 2026, a common rule of thumb is daily Wh ≈ panel watts × peak sun hours × about 0.75. As of 2026, summer in much of the US typically gives an estimated 4 to 5 peak sun hours a day. In late fall and winter you get 2 to 3, and less under trees. A 400 W array in 3 winter sun hours gives about 900 Wh, or roughly 70 Ah at 12.8 V. That nearly covers the 81 Ah example.

Generator: a 45 A charger puts back a 100 Ah deficit on lithium in about 2.5 hours. Lead-acid only takes a fast charge up to about 80 percent. After that it slows to a trickle, so the last 20 percent takes several more hours. In practice, generator owners with lead-acid live between 50 and 80 percent all trip.

Alternator: a DC-DC charger lets driving time recharge the bank without overloading the tow vehicle's wiring, and it can run a lithium profile.