Haven't weighed tongue since modification yet but I'm guessing I added about 83.4 lbs.
Battery box details $49 plus shipping are here:
Century Plastics: White Heavy Duty Battery Box - (part#: GCE-G)
The batteries weigh 66.7 lbs. each and were purchased at Costco @ $167.98 each.
Reserve capacity-20H Golf Cart 6V-GC2 Interstate each = 232
Reserve capacity-25H for the one 27SMR Interstate
12 volt = 160
I added 83.4 lbs. tongue weight and more than doubled my reserve battery capacity.