If your Switch battery appears to drain rapidly, it might be an issue with the battery indicator, and not your actual battery.
Since launch, some Switch owners have intermittently reported issues with the battery draining rapidly. This recent video from YouTube channel Switch Force shows a couple of egregious examples -- one person's battery drains from 100 per cent to one per cent in a minute:
That looks scary, but Switch owners have reported this issue for a while, and it might not be totally catastrophic. It turns out that for some Switch users, once the battery reaches one per cent, it doesn't actually turn off. One person was able to play for an additional 30-45 minutes on one per cent battery, with his total battery life lasting three hours in handheld mode. Another person said that they'd dealt with this issue since launch. One person I spoke to, Redditor theseconddennis, also said he was able to play for a while until the battery shut off while on one per cent. Today he solved the issue by turning the battery percentage display on and off, which worked for one other person.
So, if you're watching your Switch battery drain really fast, it might not be all that bad. Most users who reported this issue were also able to get their Switches repaired or replaced by Nintendo. Still, if you're freaking out, know that you might able to solve your problem with a tried and true method: Turning it off and on again.