Tim, BS. If you service your computer and it still leaks, then yeah sucks, that's life. You pay someone to do services expecting it to be right, that's why you pay them. If the shop did it right and it still leaked, the shop should be the one paying for it, not the diver. They have insurance for this sh!t if they don't want to pay for it out of pocket. The fact of the matter is that the OP paid for a service, the service was not done correctly, the OP shouldn't have to eat the consequences, if you think otherwise you are completely clueless. Also, this might be a computer that does not have user replaceable batteries, in that case the shop had to be trained by Cressi in order to service this computer, they had the full service manual, something went bad, if they refuse to replace it, they are clearly trying to hide something, that is huge red flags and they should be reported for malpractice. It is literally that simple and there is NO OTHER SOLUTION than the shop provide a replacement of the device either with the exact device if it is still in production, the current replacement for said device, or shop credit for new value of the device. Anything less than that is the shop trying to hide something and is completely unacceptable.
OP, call the shop, tell them that what happened, report back what they do. Odds are they are going to offer to replace it if they can't fix it, if they don't, let the flaming begin.