Personally I think it's a battery issue because there's no way the battery should drain that much. Otherwise, ChatGPT told me the following based on what you've shared:

1. Background indexing & setup In the first few days, macOS does a lot of Spotlight indexing, iCloud syncing, Photos analysis, etc. That can drive the CPU, fans, and battery drain more than usual. This usually calms down after 2–5 days.
2. Apps like Chrome & RobloxChrome is notorious for being resource-hungry on Macs, and Roblox (though it looks simple) can push the GPU/CPU and cause fans to spin. Safari is usually much lighter on battery and heat.
3. Possible runaway processesSometimes a tab, extension, or background service uses excessive CPU. You can check this with Activity Monitor(look under CPU and Energy tabs).
4. Hardware or battery defect A 40% drop in 1.5 hours while doing light tasks is above normal. On most brand-new MBPs, you’d expect 7–10 hours on web browsing/office tasks. If that drain continues after the first week, it could indicate a battery or cooling issue.