I have a Nauticam Canon 7D MkII housing with vacuum valve and associated electronics (no Nauticam TTL flash fire,so I can't comment on that) for two years and have done close to 200 dives with it. I always pump down the vacuum the night before I go diving and leave it pumped down with the electronics turned on until I get back from diving the next day. Typically the electronics are turned on for around 18 hours each dive day (typically two dives per day) so that would be around 1,800 hours (100 dive days x 18 hours) of electronics on time. I'm still using the original battery that came with the housing! Noting that this battery is very cheap I think you're wasting time trying to save on battery power by opening up the housing and turning the electronics on just before a dive.