Battery drain during scuba diving

I have one more: 

I lowered my mini 2 at 9:41am (additionally secured in a waterproof geocaching box) with 97% battery in a bucket with 20 liters of water. At a distance of 20cm, I still had a BT connection with my Garmin Epix 2 via the iR widget - the BT connection was only interrupted > 20cm (btw: does BT still work in close range underwater between the mini2 and the descent mk2?). At 10.41am the battery capacity was still 96%. It may of course be that it behaves differently at greater depths/greater water pressure (I have no idea/experience). It's just a few attempts more or less as "dry run" and of course they don't correspond to real underwater conditions. So was it more of a trial and error

So and now I'll spare you from further tests

No, his problem is, that his mini 2 burned 15% battery/hr under the surface,

That was not my question.

Depending on the length of the dive, the battery drain may be due to the automatic mail check. This occurs once an hour, whether you like it or not. Under water, the device will not be able to connect to the Iridium satellites. This will cause the device to continuously retry. The iR modem drains a lot of battery.

The same kind of retry will occur if there are messages or track points which have not yet been sent. You should be sure this is not the case before you put the device in the case.

That was part of my test from yesterday, placing the mini 2 in an environment where it couldn't get view of the sky, but also had tracking enabled, and an unsent message.  Even then, I only showed 3.5% / hour.  I let it go for two hours and it used 7%.

The main use case for an inReach device in scuba diving is if you come to the surface and can't make it back to the dive boat or beach. Maybe you screwed up the navigation and got caught in a current or a fog bank blew in cutting visibility to zero or the boat crew fails to count divers and leaves you behind. In that situation I would pull the device out of my pocket and lift it above the water while still in the case so that it can get a GPS fix and establish a Bluetooth connection to my watch, then push the buttons on my watch to send an SOS signal.

inReach Mini 2 has an IPX7 rating. That is incidental exposure to water of up to 1 m for up to 30 min.

I believe you would be fine with removing it from the case, turning it on or activating SOS, and returning it into the case.

The device does not need to be turned on to initiate an SOS. You can press SOS button on the device itself while off.

If the Mini 2 was on and paired, you would still need to be clear enough in your head to find the inReach widget on your dive watch and use it.

Sounds good in theory, but: if there are waves etc. it isn´t easy to fumble out the mini 2 from the dive case, and if it slips out of your hands, it's gone...

Hopefully the case is attached to the user with a bungee cord or lanyard.

If you inflate the BCD or your dry suit on the surface you become a human canoe and should be able to manipulate objects with your hands, even in large waves and wind. Someone using the mentioned dive watch and an inReach unit when heading out is no newbie to saltwater.

I have experience with tactical diving, mixed-gas, closed circuit and with comms – and was trying to imagine case scenarios.

While you may have illumination and vision in place, it’s good to have backup procedures based on muscle memory.

So, if planning to use an inReach remote or widget in an emergency, make sure you can activate the SOS with your eyes closed and freezing hands.

I think anyone here given a dive case with a Mini inside would be able to open it blindly on first attempt and press the SOS button.

Redundancy is preferred if you have the possibility and funds. I would bring my iPhone with underwater housing and a PLB as well.