1993 Johnson Evinrude "ET" 90 degrees CV Service Manual, P/N 508285, Page 371Get this manual
Handling LeadAcid Batteries
If spilled or splashed on Any part of Body
Wash with lots of Water Wash And contact Doctor, Fast! Charging Lead Acid Batteries (1) Attach and remove these cables with charger UNPLUGGED from 110 volt wall socket(Prevents shocks if the charger is defective (2) Observe correct polarity when connecting these charger Leads(3) Always charge in well ventilated areaCharging causes acid solution to give off Hydrogen gas thru the Vents in the Caps Make sure Vents are openIf clogged, pressure inside may build battery may EXPLODE