1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 15Get this manual
Out-of-Season Battery Storage 1Remove battery as soon as possible and remove all grease, sulfate and dirt from top surface2Cover PLATES with distilled water, but not over 316 in(5mm) above perforated baffles3Cover terminal bolts well with grease4Store battery in COOL, DRY place in dry carton or box5Remove battery from storage every 60 daysCheck water level and place on charge for to hours at amperesDO NOT fast charge