Moisture

after using my Tag for nearly 5 years, the battery went dead 2 weeks ago. So I went to Tag Heuer authorize dealer in Brunei to get the batt changed for $20 Brunei dollars roughly $12US. But when I ask how long the new battery will last and the Technician replied 1 yr...wtf n i ask why the oem battery last longer and he just replied thet normal if from factory...wtf answer is that. But my main issue is when i was cleaning my Tag rinsing with water which i usually do, the next morning I could see moisture condensation inside the watch. Is it because the technician didn't seal the backplate correctly? How can i solve this problem.