Pretty much any battery "can" be replaced. It's a matter of cost, if you are looking at taking it to a repair shop. Or a matter of having the right tools and experience if you are thinking of replacing it yourself.
Hello, Boo1652. The Google Pixel 3 does not have a removable battery. As mentioned by Scott5337, shops could help you remove it, but it could involve a cost. Google can also let you know if there are any options to help you remove a battery safely. If you are having issues with your battery, we can also look to see if there is warranty on your device. Please send us a Private Note, and we can look at more details.