I'm not sure about the battery, as it's brand new, and I don't have a need to replace it yet, but the RAM and SSD are both user replaceable on the XPS15. The battery looks like it would be a fairly easy swap as well, as long as you could source the new one.
Thats the most difficult part. Original battery costs a fortune (some of them cost almost half of the new basic laptop). And if you decide to get a third party alternative - its basically a russian roulette, you never know what you gonna get, most of them are just terrible and barely last couple months
