i have (5) of these for a total of 675 ampHrs
{i know you only have room for two} if they fit height wise}
Dimensions
"Product Width 6.85
Product Height 10.87
Product Length 13.31
Net Weight 102
Amp-Hour 135
Model FIAMM 12FLX500"
you might think about checking craigslist for surplus AGM telco server batteries
mine are FIAMM high rate, 135 ampHr at 8hr rate (even more at 20hr) 102# each
about $300 new per item when buying a pallet of 16, mine were less than $99 each surplus, love them
other areas of the country have similar batteries available
around here its usually the solar and marine dealers in San Diego
https://www.wholesalebatteriesdirect.com/fiamm-ups-batteries/66616-fiamm-12flx500-12-flx-500-135ah-493wpc-high-rate-ups-standby-battery.htmlsomething to think about, instead of dropping a bundle on new lifelines
these batteries have been in daily full time use for 10 months