I've had mine last 12 hours a couple times. I don't have Strava segments on.

If your backlight was set to always on, that's your reason why.

However, the 520 Plus is not known for infallible batteries. Mine eventually got down to ~3 hours using all the recommended settings from Garmin except for using 1 second recording instead of smart. It maybe got 2/3 the advertised battery life when new.

40% backlight is quite high. I generally go with 10% backlight.

I found the life of my 520 Plus was pretty much as stated (approx. 15 hours in normal conditions), but that it took a big hit once I connected a Varia radar. So much so that I would often finish a 200km ride with <10% left, and 300km rides required a lot of juggling with chargers, etc. Then switched to a 530, and much happier with battery life.

I have since discovered that the Backlight Timeout is a major factor with Varia alerts, and cutting the timeout to 15 seconds has significantly improved head unit battery life.

Also, leaving it on the mapping screen means the map has to constantly re-render as you ride along, which is processor and battery intensive. By all means scroll to the map screen for a nav check whenever you need to, but if you are JRA, leave it on a data screen.

Ah. Maybe the backlight is the issue. I’ll have to check that setting