1989 Johnson Evinrude "CE" 9.9 thru 30 Service Manual, P/N 507754, Page 282Get this manual
Battery Charging Boost charge 12-volt batteries at 50 amperes for 20 minutes (1000 ampere minutes)If the charger will not give this rate, cha rge for an equal number of ampere minutes at best rate available DO NOT boost battery more than this amount for the "light load test" If batteries are to be fully charged by means of quick charger, the charge rate must be "tapered" (reduced to safe limit) when the electrolyte temperature reaches 125 (52 C), or when gassing becomes excessiveFailure to do so may harm the battery If the battery is to be slow charged, adjust electrolyte to proper level