Garmin, you should definitely patent this! ;)
I am using the Garmin Instinc Solar with cardio, GPS navigation, activity tracking turned on for 5 days and the Garmin predicts I can do that for an infinite number of days! (4 days in a row!)
Obviously, it's a bug, battery life is actually going low by nearly 20% every day and is close to empty by the 5th day.
I understand it is difficult to predict batterie life vs usage (as discussed in some other threads). You may be off by few days. But when the consumption is always, at all time, higher than the recharge, how can you be infinitely wrong?
Some screen shots to illustrate.
No USB charge since day 9.
On day 10, no sun recharge since 11 hours, the estimage is already wrong but lets wait.
On day 11, again no sun recharge since 11 hours, battery drawn during the day much more than it could solar charge, but the life estimage gets higher!
Same story for the next 4 days.
By the way, that's with firmware 17.50