Originally Posted by w8keluv
House battery. But also want the option to charge via alternator or solar
I went through this for my build, in fact I bought an OEM box and then sold it. The OEM battery boxes are for Group 65 batteries. A Group 27 will go in the box but it's too tall. Some have modified the box to let it hang lower and remove the cover (search this site)
The largest size I figured would fit in the location is a Group 31, mounted on its side for better ground clearance. But that is a totally custom battery tray.
I could not find anything on line to mount a bigger battery there.