What are the signs that the battery is dying?

About Mac notebook batteries - Apple Support

Several things can happen. The battery icon in the menubar will show an alert. Notifications may also alert you.

Short runtimes, a high cycle count (see: Determine battery cycle count for Mac notebooks - Apple Support ), or a steep loss in power while off or sleeping can indicate battery failure.

⚠️ However, usage patterns and poor software decisions can shorten, runtime.Google Chrome is a know drainer of notebook batteries. Even with other browser, leaving certain web pages open the background ca run down the batery at an aceelrated rates. I can reproduce that at will on my MacBook Pro by leaving the Amazon home page open in the background.

Useless anti-virus and even more useless "cleaning" apps WILL short runtimes. I've work a number of posts here where the OP had 2-hour runtimes on relatively new computers. They had installed anti-virus and/or cleaning apps. In every case, simply deleting all the fearware restored runtimes to 6 or more hours.

Determine battery cycle count for Mac notebooks - Apple Support

About Mac notebook batteries - Apple Support

Battery health is <80% (health = current cull charge capacity ÷ battery design capacity). Easiest way to determine this is with a utility like iStat Menus or CoconutBattery.

Apple menu > About this Mac > System Report > Power indicates that the Condition is Service battery.