Not sure if the photo will show up posting from my phone, if not I'll fix it later.
Anyway I purchased an AGM battery sized H8...92 amp hours and mounted it under the rear bunks in our ST27BH.
AGM batteries don't vent as part of the normal charging process (no liquid, can be mounted any direction), and only have an over pressure relief. That being said I may still run the vent tube outside.
My old battery was 48 lbs and removing it reduced my tongue weight by 40lbs. Installing my new 58 lb battery to the rear further reduced my tongue weight another 25 lbs. So all together I saved about 65 off the tongue.
Keeping the battery inside should also keep it warmer slightly increasing its capacity in cold weather.
I hit the scales the other day before the mod, and my tongue weight was about perfect......but with lots of stuff loaded in the rear. Moving the battery allows me to utilize the front "basement" area with heavier things like firewood or tools. The basement BTW adds 60% of the items weight to the tongue. So a 20lb toolbox adds 12 lbs to the tongue. In my case I can now put 100lbs of additional stuff in the front and keep the same tongue weight that I had before.
Another reason I moved it is I'm contiplating adding a second battery and there wasn't room on the tongue for that.