large SLA's might be 19Ah, 12V 50mΩ when new.
often n*Ah*ESR remains fairly constant for n cells.
So as battery Ah reduces with aging, ESR also rises and is a multiple of 6 cells in series.
But all it takes is the weakest cell to break the whole string.
Assuming Vbat drops to 8Vmin or 0% SoC for gel-cell, and alternator too high at 14.5V ,
Gel cell ESR rises rapidly below 10% SoC which limits surge current.
But as SoC rises above 10% Vbat might be 11V (EST.) Wh
(14.5-11) *0.05Ω= 70A
So a fresh new battery not charged might blow the fuse, so we might consider a 30A
PTC cheap in series, Aka Polyfuse, unless we get the SLA part number and make to know better