Some of the 4A per bank chargers have distributed charging. What that means is that all 8 amps can go to one bank if the other doesn't need it.
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I use the 3 bank charger and love it. You get back from the lake and plug it in till leaving for the next trip. Wonderful!
Dual Pro has been a good company to work with. Good warranty and they back up their products.
Got the Dual Pro 3-bank on mine and love it, plug and forget.