Horrible battery life on iPhone 6s?

I ordered an iPhone 6s off eBay a week ago. The battery health is at 87% so the phone is supposedly in decent shape, but the battery life is terrible. I listened to some podcasts last week for an hour and a half, took my battery from 100 all the way down to 30. The battery has dropped from 25 to 12 in the last 10 minutes or so? I’m not watching videos or anything, just listening to Spotify in the background destroys the battery. Is the phone faulty? I’ve turned off location services and background app refresh for most apps, doesn’t help much. I’m running iOS 12.1.4.

thanks.