How can I use my 12' MB 2015 with AC power only? (No battery)
Leaving your MacBook plugged in is not "abuse". Apple's laptops contain power management that prevents any problems. Even while plugged in, you may see the battery % indicator change from between 93% to 100%.

https://support.apple.com/en-me/HT204054#notfull


  My battery won't charge to 100% 
  
  
    Occasionally, the battery might not show a full charge (100%) in
    macOS, even after the power adapter has been connected for an extended
    period of time. The battery might appear to stop charging between 93
    percent and 99 percent. This behavior is normal and will help to
    prolong the overall life of the battery.