Service battery

"Service Battery" means just that: Check the condition of your Mac computer's battery - Apple Support.

• Service Recommended: The battery's ability to hold charge is less than when it was new or it isn't functioning normally. You can safely continue to use your Mac but you should take it to an Apple Store or Apple-authorized service provider to get your battery evaluated.

Get it fixed: Mac Service and Repair - Official Apple Support

If it says "Service Battery" then it means an internal hardware fault has been detected within the battery so it should definitely be replaced.

However, Apple recently changed the way the battery condition is displayed with macOS 10.15 Catalina so if it says "Service Recommended" this may just mean the battery capacity is not able to run the laptop for as long, but it may also mean an internal fault has been detected. I really don't like the new way Apple is reporting battery condition as users can no longer distinguish between an actual hardware fault and just a battery unable to run for as long.

If the condition is "Service Recommended", then run the Apple Diagnostics to see if it reports a battery failure. Usually the Apple Diagnostics will be more accurate than the battery condition reported by macOS although I found the old reporting method to be very accurate.