Posts: 2754
Location: Mauston, Wisconsin | When you have lots of electronic loads, sonars, GPS, stereo radio/dvd player or marine radio etc. running off your starting battery, you need a dual purpose marine battery. Its a compromise between a starting battery (high rate) and a trolling motor battery (low rate), Todays "smart car" electronics turn off the headlights, dome lights etc, after you exit the vehicle - those are low rate discharges. Much like your electronics. Try that with a 60's or 70's car or your boat, and you will be looking for jumper cables.
A marine battery isolator doesn't do anything to help unless you add a second battery (low rate) for your electronics, then its a good solution.
A two battery isolator is really just two (2) high current diodes configured so they are reverse blocking and mounted to a heatsink. The two batteries can be charged from the alternator and cannot discharge each other - Its actually pretty simple, and can be built with off-the-shelf parts -> two 30A-100A 12V diodes depending on your alternator rating and a heatsink plus a little hardware.
Need a 3 battery isolator- add another diode.
Have fun!
Al
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