What Size Battery Bank Do I Need for an RV Air Conditioner?
Running RV air conditioning from batteries is a large bank because the running watts are already a three-figure amp draw at 12 V.
Direct answer: Honda lists a 13,500 BTU RV air conditioner at 1,800 W running and 2,800 W starting, which is 150 Ah per hour at 12 V, and a 15,000 BTU unit at 2,000 W running and 3,300 W starting, or 166.7 Ah per hour (Honda wattage guide). Champion lists a 13.5k unit at 1,500–2,000 W running and 2,800–3,500 W starting (Champion wattage chart). A 200 Ah bank, the minimum the inverter rule gives a 2,000 W inverter, covers the first hour of the 1,800 W unit and leaves 50 Ah (Battle Born inverter guide).
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Honda publishes two BTU classes. Champion publishes a 13.5k range. Neither chart says the air conditioner runs all afternoon, so the bank below is per hour.
Stay in amp-hours per hour until you know how long the compressor will run. Watts × 1 hour ÷ 12 V is the running watts divided by 12 (Battle Born battery-bank guide).
Honda 13,500 BTU: 1,800 ÷ 12 = 150 Ah per hour. Honda 15,000 BTU: 2,000 ÷ 12 = 166.7 Ah per hour (Honda wattage guide). Champion's 13.5k running range is 1,500–2,000 W, or 125–166.7 Ah per hour (Champion wattage chart).
A 200 Ah bank is the Battle Born figure for a 2,000 W inverter (100 Ah per 1,000 W). Against the 1,800 W Honda unit, 200 Ah supplies the 150 Ah first hour and leaves 50 Ah, which is not a second hour (Battle Born inverter guide; Honda wattage guide). That is the honest version of "running RV air conditioning from batteries": the bank that satisfies the inverter rule is still about one hour of cooling at these running watts, before other loads.
A 3,000 W inverter would call for 300 Ah by the same rule. 300 ÷ 150 = 2 hours of the Honda 13,500 BTU running load, and only if nothing else is on and the battery is the manual's 100% usable lithium (Battle Born inverter guide; Battle Born 100 Ah manual). The surge rating of that inverter still has to clear the start watts below. This page does not assume a 3,000 W continuous rating includes a 3,300 W or 3,500 W surge.
Current at 12 V equals those per-hour amp-hours: 150 A running for the 1,800 W unit and 166.7 A for a 2,000 W unit. Both are over the 100 A continuous rating of one battery, so at least two batteries in parallel are required to keep each under 100 A (Battle Born 100 Ah manual). The guide also recommends a minimum of two batteries for larger inverters in many 12 V systems (Battle Born inverter guide).
Starting current is higher. 2,800 ÷ 12 = 233.3 A, 3,300 ÷ 12 = 275 A, and 3,500 ÷ 12 = 291.7 A. Two batteries at the manual's 200 A for 30 seconds are 400 A together, which covers those start currents as a battery limit. The inverter still needs its own surge rating at or above the start (Battle Born 100 Ah manual; Battle Born inverter guide).
A current surge limiter may be needed around 3,500 W and above (Battle Born inverter guide). Honda's starts are 2,800 W and 3,300 W, under that line. Champion's start range reaches 3,500 W, which is the line itself.
Lead-acid at about 50% depth of discharge doubles the nameplate. One hour at 150 Ah usable is about a 300 Ah lead-acid bank (Battle Born chemistry guide). Two hours would double that energy again (Battle Born battery-bank guide).
A soft start is a product search on this page, not a published wattage reduction. None of the source charts give a lower start wattage after a soft start, so the table stays at 2,800–3,500 W until a meter says otherwise.
Charging from a generator can shrink how many hours of cooling you must store (Battle Born battery-bank guide). That wattage question is the generator page linked above.
Add the rest of the RV on the battery bank calculator before buying a bank sized only for the air conditioner.
What size battery bank do I need for an RV air conditioner?
Per hour, Honda's 13,500 BTU unit at 1,800 W is 150 Ah at 12 V, and the 15,000 BTU unit at 2,000 W is 166.7 Ah. Champion's 13.5k range of 1,500–2,000 running watts is 125–166.7 Ah per hour (Honda wattage guide; Champion wattage chart).
Why is 200 Ah still a short run?
A 200 Ah bank is the minimum the Battle Born inverter guide states for a 2,000 W inverter. The 1,800 W Honda unit uses 150 Ah in the first hour and leaves 50 Ah, so it does not finish a second hour (Honda wattage guide).
Do I need two batteries and a surge limiter?
Two batteries, yes. Running current is 150–166.7 amps, over one battery's 100 amp continuous rating, and larger inverters are recommended with at least two batteries (Battle Born 100 Ah manual; Battle Born inverter guide). A surge limiter is the 3,500 W discussion: Champion's start reaches 3,500 W, while Honda's starts are 2,800 W and 3,300 W (Champion wattage chart; Honda wattage guide).
What does lead-acid change for one hour?
One hour at 150 Ah usable is about a 300 Ah lead-acid nameplate, because flooded and AGM batteries are typically limited to about 50% depth of discharge (Battle Born chemistry guide).