Series 3 under warranty not supported

It is very rare to get the nominal battery life in a real world usage, because Apple's 18 hour figure is the minimum duration for a new battery operating under standard test laboratory conditions. You are working in the real world and you are almost certainly not reproducing the test routines. My real world experience of Series 3 is that most days I would have >60% remaining after about 20 hours usage. Some days I would be down to about 30% remaining just because I was working under different usage and cellular conditions.

I can't comment about the rejection by Apple Store staff because I was not there, I can't verify the warranty status of your Apple Watch from Apple's records, and I was not part of the conversation. However, I would expect Apple to honor warranty and any AppleCare+ cover you might have purchased.

I suggest you start by checking the officially recorded warranty status for your Apple Watch. You will need the Serial Number, entered into the page at Check Your Service and Support Coverage - Apple Support

With warranty cover confirmed, go confirm the exact terms of your warranty by drilling down from Legal - Hardware Warranties - Apple. The exact content varies according to where you live, so you will have to find the correct links to follow.

Finally, with all the relevant knowledge to hand go to https://getsupport.apple.com/ and either re-open your previous service case, or start a new repair case.

The Apple Watch Series 3 isn’t listed as vintage yet, vintage is when service support typically stops due to the hardwares age. See Apple Watch Service & Repair - Apple Support which links you to Obtaining service for your Apple product after an expired warranty - Apple Support

However, this could vary by country, the Genius May have misspoke, you misunderstand, have a different model, or not actually have a warranty like you thought.

I would double check your coverage and model at Check Your Service and Support Coverage - Apple Support to make sure you actually have a Series 3 and warranty.

Lastly, where did you buy the Watch from?

405Oklahomie wrote:

It’s still under warranty till July because I checked it and it is a model three. I was using a workout service called future and they needed me to have an Apple Watch to track my data. They said they can send me one with the welcome package so I just paid them and they bought a new one and send it to me. Still with the plastic cover on the packaging and everything. The battery used to last me a whole day and then about a month and half ago, it just went down to 12 hours (if I do nothing) and like 10 ish if I go workout or anything. I’ve been fine with it but when my workouts started ending early without me ending it, I decided I need it fixed. The other thing is, I have 8 days remaining to buy apple care on it but I don’t understand what apple care will cover if the genius at the store said they’ve stopped supporting it and can’t do anything

Did you check the warranty with Apple as explained above? Or are you going by the receipt you have from "Future"? If the latter, that may be the source of the problem. The warranty on the watch would have started from the day Future purchased it from Apple, not the day you purchased it from Future.

I would suggest then, as recommended above, that you contact Apple directly to resolve the issue.