How do I know if my laptop battery is dead?

Sep 4, 2018
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So whenever I start up my laptop without my charger plugged in, the battery icon would sometimes show that it's at 0% and then shut down. I would then start it up again with my charger plugged in and it would then show that it's at 100%. Now this doesn't happen every time I start it without my charger since sometimes it starts up normally without this weird problem.

So is this a problem with my battery or is this something else?