A battery rarely warns you politely. We test it under load before replacing anything.
A slow crank on a cold morning is the usual first sign, and by then you are often days away from a no start.
We test the battery under load and check the charging system in the same visit, because if the alternator is the real culprit, a new battery only buys you a few weeks.
We also check the terminals and grounds. A surprising number of no start calls are corrosion, not a dead battery.