I had the identical problem on my maiden voyage, a 300 mi one-way trip to see the eclipse last august. I had not even thought about bolting my lead-acid battery down, and I paid the price.
I fortunately had a scissor jack with me along with a few short pieces of 2×4, so I was able to jack the galley flat back in place from inside the cabin for the return trip (I also removed the battery).
for the repair, I put a strip of fiberglass tape both on the “outside corner” of the joint inside the cabin, and the “inside corner” inside the galley. I have a battery hold-down arrangement in mind to try out, but since I am using my trolling motor battery I will likely spring for a lithium battery.
slightly off topic, but I helped my son outfit a sprinter for living off the grid, and on the recommendation of others who had done the same thing, we purchased a 100Ah LI battery from battlebornbatteries.com. all they make are LI batteries for off-gridders. they are roughly Group 27 size, and as has been noted by others, they can safely be discharged to almost 0% charge, so you get the full use if 100Ah, instead of discharging only to 50% with a lead-acid deep-cycle battery.