Forerunner 945 battery issue

Could be any of many factors. How the watch is used, IQ Connect apps (developers will tell you this is impossible, but I proved it to one by both of us testing with and without the IQ app), charging to often before letting the battery nearly drain (the battery will learn what it thinks is a full charge) or a defective watch. I have two friends that got their 945's within a couple of weeks of me (all in May). We pretty much use them the same way. Smart recording, backlight at 10%, and a few IQ apps if any.  No issues between the 3 of us. There's 5 people posting with issues. I doubt that's even 1% of units sold.  Unfortunately, it's more likely you're unlucky and hopefully you'll be able to get it resolved.

No problems at all here. 

My 945 is consuming 5% per day. HR is always on, smartwatch mode is always on, pulse ox is off, backlight comes on after sunset (at 5%). 

How/where do you get that Screen/Info?

That’s a widget called Battery Monitor

After 12h

I have a huge problem with my battery since the update to 2.5. It wa 100% charged at 6am this morning, now 2 hours and 20 mins later it's on 43%, and that's without any activities or GPS use. Have tried powering off and back on, but not made any difference. If it remains like this then it will be sent back as faulty.

Hi Sime11 - do you have the wifi on. Turn auto updates off.  What's happening with the HR Leds - off or flashing?

are you running any custom watch faces? I'd take everything back to basics and see if it makes a difference?

No custom watch faces, everything is pretty much standard apart from going through the usual setup process to setup up bluetooth connection to phone, wi-fi etc.