According to multiple sources, Nintendo of America is allowing anyone that purchased the older Switch model after July 17, 2019, to trade-in their unit for the upgraded one with better battery life. For those unaware, a hardware refresh was released into the wild last month that increased the Switch's battery life from 5.5 hours to around 9 hours in portable mode. Since the announcement came out of nowhere, many people may have purchased the older unit unaware that a better one even existed.
The discovery came from a Reddit thread that asked about the possibility of trading in a launch day unit for the new one. Nintendo told user DarthMewTwo that only consoles purchased after July 17 would be eligible for exchange. YouTube channel GameXplain confirmed the report, as did outlet Digital Trends. There are no strings attached, other than Nintendo requiring you to pay postage for shipping.
If you think this may apply to you, you'll have to first confirm you have the older Switch model. The easiest way to tell is if the packaging contains a white background as the newer model is in a mostly red box (like the header image). If you've thrown out the box, then check the serial number. The newer models all start with "XKW" for their serial number. Once you've confirmed everything, send an email to Nintendo's support address and they'll give you all the information you'll need to get the newer Switch revision.