So just like any other modern device, then.
The Nintendo Switch battery is not user replaceable, unlike any prior Nintendo device until now- but if your battery starts to degrade, and you want or need it replaced, you won’t have to buy an entirely new Switch system- Nintendo has confirmed that it will offer battery replacement services for the Switch. You will just have to send your Switch in to an authorized Nintendo service center, and they’ll replace the battery for you.
This sounds about right- and is actually how battery replacement is handled on just about any modern device. iPhones, HTC phones, Samsung phones, Surface tablets, iPads, and even MacBook laptops, all are similar, as well as Sony’s DualShock controllers, and PS Vita- so this should be pretty commonplace for most customers at this point.
The Nintendo Switch battery life is due to last 3-6 hours on a single charge, which is in line with the battery life for a PS Vita or a Nintendo 3DS.