I don't know of an alternative player, much less one that would not have battery issues similar to your iPhone. I realize an alternative player could have battery issues but the players I've been looking at cost less than the replacement battery I got for my iPhone 7 ($79.00 plus tax)!
However, the advice you received about your iPhone battery is badly outdated and likely a part of the problem. Good to hear
In iOS 13 and later, Apple added optimized charging
that manages the charging process to extend battery life, when I set my iPhone on the Qi pad at night it notifies me that "Optimum charging" is in effect and what time the phone will reach full charge. My three-year-old iPhone is on charge all night roughly 365 nights a year and is rarely discharged below 50%. I forgot about Qi or Mag chargers because when I looked into them I had a 5s and they couldn't accommodate it. Now I am interested. I've seen them for $20.00 or less, so I will start with that.
According to Settings > Battery > Battery Health in iOS 16 beta, the battery still has 100% of the capacity it had when new, and a calibrated Battery+ app appears to confirm that estimate as well. According to what I've read version 15.5 cause battery drain and not just temporarily so I've opted not to upgrade at this point in time.
I prefer Qi or Mag chargers to plugging, not only for the convenience, but because they charge a bit more slowly and the battery never overheats. Although Apple approves plugging in to higher capacity chargers for faster charging, I avoid them if possible because of heating -- but that is my prejudice and not confirmed elsewhere. I have always made it a practice to periodically audit battery usage and adjust iOS and app settings to minimize unnecessary battery drain. This PC Mag article
and this iMobie article
have numerous good tips on battery management. I will read the articles. Thanks.
If your iPhone battery is showing signs of degrading, you might be better served by spending $60 on a new iPhone battery and changing your battery management practices.