Our Samsung Galaxy S5 Actives have user-replaceable batteries, and they really would benefit from some new batteries. We purchased them as new old stock about three years ago, so it sounds about the right time for a replacement.I put a new battery in my Samsung Galaxy S7 Edge. It's 4 years old but still is a fine phone. Had to unglue the back cover and disassemble half the phone. But all is good now!
Unfortunately, the stock battery replacements may be approaching the age of when these phones were released six years ago. People complain about getting a "new" battery, only to find it doesn't hold a charge as well as their older, less than 100% healthy battery. Probably been sitting in storage for too long. And the 3rd party batteries seem to be a huge hit and miss with them, mostly a miss.
As it is, the S5 Actives are stuck at Android 6, as the chipset can't be upgraded beyond that. In addition, AT&T has refused to provide the patch for BlueBorne. It's listed on Android's site, but AT&T won't filter it through to owners. Thankfully, we don't use our phones for logging into *any* online personal account, nor are they used for wireless payment.
AT&T is probably trying to force users like us to upgrade to a new phone through them and more expensive service. We'll likely find a different phone with a different service provider before we do that. Sounds like I have my "What did you do today" entry coming soon.