The post on this forum for V18.23 says the battery life estimate under Battery Saver was fixed.
I have observed very low estimates in the past, so I usually just ignore the estimate on my non-solar Edge 1040.
But I installed 18.23 today after my ride, so I decided to check whether the estimated battery life was different. Is it ever! My battery is at 75%, and the estimated life is 75 hours. Past usage has shown me that I can get about 55 hours between charges (letting the battery go down to between 5% and 10%). If the battery is at 75% charge, that means I have ridden around 12 - 15 hours since charging. So the estimated life seems a little optimistic.