I want to connect a lead-acid starting battery to a bank of deep discharge batteries on my boat via a diode. The purpose will be to let the start battery charge from the same source, but to not back feed. First, I'm unsure how to rate the diode. 12v is maximum voltage, that's clear. But should I rate the diode equal to the max amps of the charging source (75 amps). I fear surges of higher currents when connecting batteries of unequal charge state. In actual use, it will probably conduct 20 amps for 3 seconds after each start of my diesel engine. It only takes about 400 joules to start the engine. Second, the diodes I find online seem to all have tiny pins made to solder into a printed circuit board, even though some claim to be rated 75A. It seems ludicrous to connect such a tiny pin in series with 6AWG cable. Also, I was also taught long ago to never use solder in power circuits because of safety reasons. What is the right diode for me?