Torn on what to do

I currently have the iPhone 13 Pro Max. I am going to upgrade since the battery life on this phone sucks now. I'm just torn on getting the iPhone 18 Pro Max or getting the iPhone Duo. Price is not an issue for me. I always lean more towards big phones since I have relatively big hands. I like the duo because it's something new and I've wanted a foldable phone but want to stay with Apple since my wife and kids have Apple and can keep FaceTiming and sharing locations. I really want the duo I just feel like I will ultimately regret getting it, being that it is the size of a passport book. I held my passport book in my hand and it just felt too small for me, but the foldable phone is something I'm really interested. I had a Pro max before so nothing breathtaking for me with the iPhone 18 pro max. Just need some recommendations as to what you would do in a similar situation.