The screw holes do not align 100%. Dont tighten all the screws as you re-insert them, leave just a little bit of play so that you can push the battery slightly until all the screws fit nicely, then tighten them. A little bit of DIY wisdom helps here. :-)

In my 6th generation X1 Carbon there are two wires that are routed on the edge of the battery and have to be moved out of the way. These are antenna cables, be gentle with them, kinks and indents change their high frequency properties and may lead to problems with your WIFI.