I didn't see this thread earlier.
Last year the TARC team I mentored eventually broke the battery holder on every altimeter they flew, both Perfectflite and Adept. The cause was the rather sudden arrival from undersized streamers. It took a lot of test flying to find the right size and folding technique to get an acceptable descent time and apparently that's putting stresses on the altimeter that are pretty much at the limit when all goes well. The only good solution is to send the Altimeter back to Perfectflite and let them replace the battery holder. Don't hold your breath waiting to get it back. This is TARC season and they will be busy.
With the repaired altimeter, install with the spring in the battery holder facing up. That way you will not lose continuity on liftoff because of the spring compressing, but you will have it to absorb some of the shock on a hard landing. Pad the altimeter. We were installing both soft and stiff foams to progressively cushion the altimeter, but make sure the foam does not cover the pressure sensor. Basically, we mounted the altimeter in a BT50 tube installing things in this order : soft foam, stiff foam, altimeter, stiff foam, soft foam. The stiff foam was cut into plugs that fit the tube. This is pretty much what the instructions tell you to do.