Finally replaced the battery in the GXP today (was still OEM). Thx @DeepBlueGXP for the videos, very helpful.
I will note that the top plug on the fender liner is a two piece unit in my case, where the middle part needs to be pulled out (or pushed from behind), then the second piece collapses on the back side and can be pulled out as well. IIRC, these were part of a fender liner update completed under warranty.
To anyone replacing the battery, trim removal tools are pretty much needed to get the fender plugs out.