A CPAP is a small, steady load. The bank is set by hours asleep, not by inverter surge.
Direct answer: Champion lists a CPAP at 30–60 W, and a heated CPAP at 60–120 W, with no separate starting watts (Champion wattage chart). Using 8 hours as the example night, that is 240–960 watt-hours, or 20–80 Ah at 12 V (Battle Born battery-bank guide). A second night doubles those amp-hours, and lead-acid at about 50% depth of discharge doubles the nameplate again (Battle Born chemistry guide).
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Champion publishes the watts. The watt-hour and amp-hour steps are Battle Born's sizing method applied to an 8-hour example. Nothing here is a sleep study or a runtime test from this site.
Amp-hours at 12 V are watt-hours ÷ voltage. 240 ÷ 12 = 20 Ah, 480 ÷ 12 = 40 Ah, and 960 ÷ 12 = 80 Ah (Battle Born battery-bank guide).
Two days off-grid doubles the capacity (Battle Born battery-bank guide). A second night takes the one-night figures to 40 Ah, 80 Ah, and 160 Ah.
A 100 Ah lithium battery in the manual is 12 V, 100% usable, and rated 100 A continuous (Battle Born 100 Ah manual). An 80 Ah heated night fits in that one battery. Two heated nights at 160 Ah do not: 160 ÷ 100 = 1.6, so the count rounds up to 2 batteries (Battle Born battery-bank guide).
Lead-acid and AGM are typically limited to about 50% depth of discharge, and a 100 Ah lithium battery is compared with a 200 Ah lead-acid bank (Battle Born chemistry guide). One heated night of 80 Ah usable is about a 160 Ah lead-acid nameplate. Two heated nights, 160 Ah usable, are about a 320 Ah lead-acid nameplate.
The manual also lists 3,000–5,000 deep discharge cycles for this lithium battery (Battle Born 100 Ah manual). That cycle range is why a nightly CPAP load is usually argued on usable amp-hours, not on replacing the bank after one season.
A CPAP is often one line on a larger van list. The daily total belongs on the battery bank calculator.
For an 8-hour night, Champion's 30–60 W range is 20–40 Ah at 12 V, and the heated 60–120 W range is 40–80 Ah. Watt-hours are watts × 8, then divided by 12 volts (Champion wattage chart; Battle Born battery-bank guide).
What about two nights without charging?
Double the one-night bank. The Battle Born battery-bank guide says two days off-grid doubles capacity, so a 120 W heated night goes from 80 Ah to 160 Ah at 12 V.
Double the nameplate. About 50% depth of discharge means one heated night of 80 Ah usable is about 160 Ah of lead-acid, and two nights are about 320 Ah (Battle Born chemistry guide).