Apple claims that the battery life of the 13 is a bit better, but I don't know how much you'll actually see. If you just want something that'll last 3 years, the 11 will likely last that long, but possibly no longer. The 13 should last longer and also has a brighter, higher-res display. If you can afford it, get the 13. However, the 11 would be a decent choice, too.

You can compare the two here: https://www.apple.com/iphone/compare/?modelList=iphone-11,iphone-13,iphone-14-pro

Side note: you probably don't care, but the 13 supports FaceID with mask; the 11 does not.