Xiaomi 15 vs Xiaomi 17 global - battery life

Currently using Xiaomi 15 but thinking about moving to 17 due to battery. I just wonder how is it possible that the battery size of the global variant is roughly 20% larger than X15 but for some reason, I saw some tests where X17 has got like 45% better runtime? Elite Gen 5 isn't that much more efficient than Elite Gen 4.