I found this in the iFixit teardown at the end.
AirPods Max Battery: "Made by Sunwoda, the two cells are wired in parallel, with a total capacity of 664 mAh and 2.53 Wh total energy at 4.35 V. Each cell measures approximately 5.7 x 20 x 28 mm."
Comparison:
Bose NC700 Battery: "This is right in line with the 2.39 Wh cell in the Bose NC 700 wireless headphones, which also promise around 20 hours of listening time."
Sony XM4 Battery is bigger: "Sony WH-1000XM4s offer a longer, 30 hour listening time, with a correspondingly larger 4.1 Wh battery driving them."
AirPods Max Battery: "Made by Sunwoda, the two cells are wired in parallel, with a total capacity of 664 mAh and 2.53 Wh total energy at 4.35 V. Each cell measures approximately 5.7 x 20 x 28 mm."
Comparison:
Bose NC700 Battery: "This is right in line with the 2.39 Wh cell in the Bose NC 700 wireless headphones, which also promise around 20 hours of listening time."
Sony XM4 Battery is bigger: "Sony WH-1000XM4s offer a longer, 30 hour listening time, with a correspondingly larger 4.1 Wh battery driving them."