Hmmm..I was about to say it would be hard to harm things. You would need to have the entire battery submerged underwater to cause a problem. Get some paper towels and try to absorb some additional water and leave it open overnight - maybe in the sun for a day and the remaining water should evaporate.
Now about the liftgate - you mean the rear hatch, right? Very odd that it should have suffered harm from this ...but perhaps some wiring or electronics were harmed. Best thing is not to try to operate the hatch electronically until everything has dried out completely. Sometimes electronic components start working after a bath if you allow them to dry completely.
Have you checked the fuses? I think there is a block behind either the right or left access panel in the cargo area - search for fuse on this forum. It may be just the fuse is blown. If it is not that, then my thought is that some electronics associatedw ith the hatch were compromised.
Oh...last thing - go get a cargo mat Mine in my E83 X3 contained spills from both solid (dog kibble) and liquid (sodas, water, etc.) quite nicely.
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