To answer your question is it normal always? No not always and only a doctor can tell you for sure.
It can be perfectly normal for one testicle to be larger than the other however if you notice other symptoms such as, it feels larger because of fluid build up or if it feels firmer than the other or you've found a lump on the testicle or pain in the abdomen groin or back at the same time then this is something to have your doctor look at. I hope this helps.