I currently have a fenix 5 with mapping.. love it but it the battery only lasts about 5-6 hours, considering a 6s for longer battery life running hiking maps, can I get thru a 12 hr hike?

The watches you mention don't have real mapping, but has a display of the route. But it should give a longer battery life than 5 hours in any way. So it may have a degraded battery.

My advice is switch to a different data screen when not needing the map.

Constantly re-rendering the map screen as you move along is processor (and therefore battery) intensive. This applies to the 5X as much as the 6. Rather than the expense of a new watch I'd recommend using a standard data display as your main display while hiking, and just scrolling to the map display when you need to do a navigation check.

I'd also recommend looking at some of the other major power drain features on your current watch to see if you can extend the battery life:

* Using GPS+GLONASS/Gallileo uses about 40% more power than GPS alone. Using a 2nd constellation can be an advantage in a narrow valley with a limited horizon to "see" the minimum of 4 satellites, but with an open horizon, there is no real advantage over GPS alone.

* Backlight. Each 10% of backlight brightness uses about 1.5% of battery per hour (that's 15% of battery per hour at full brightness), and in bright sunlight you can't really tell whether it is on or not - you may be using more backlight than you think, especially if it is set to come on for alerts. I'd recommend adjusting the backlight brightness down to 5-10%, setting it to come on only After Sunset, and shortening the timeout. You may also want to turn off backlight on alerts, and have it come on for gesture only.

I have a 6s Pro. I'd say yes, you would get 12h of continuous hike recording with full features enabled. That's exactly the reason why I switched from a 645.

You absolutely won't get those 24h declared from Garmin when using the watch as you should. I've set mine to record every second, GPS+Galileo, backlighting off (I usually hike after sunrise and before sunset), Bluetooth ON, LiveTrack ON and often I keep the map shown with high details and quite zoomed in (the auto zoom is quite useless for me as it doesn't help with nasty turns on less visible forest paths).

12-16 hours is a reachable goal if you don't spend that much time touching buttons.

Did you find these power consumption percentages posted somewhere, or is this from personal experience?  I know using GLONASS and Galileo will increase power consumption, but I didn't think it would be by 40%.

It's nothing close to 40%.

I didn't think so.  Not in my use case at least. 

This not normal...you should also consider if you use the watch daily for the past 3 years battery should lost some of its capacity. (F5 released 4 years ago). I would go for F6 Pro instead of 6s if you need more battery. 

Personal experience (that was with my F5, which was referenced by the OP) - took consumption from 4% per hour to 5.5-6% per hour. Haven't crunched the numbers with my F6 - you are welcome to do so and post the numbers if they are materially different.