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Hi guys. I am thinking of getting a second 275ah deep cycle gel sealed battery, at 12 volts. Thinking of using 3 100 watts solar panells connected in series, with a total Voc of 64 volts. My question is if a Victron 75/15 Mppt solar controller is a good option or capable of well charging and maintain that battery, in a 12V solar system?
Your MPPT 75/15 is undersized for 300W of solar modules. At 12V, 300W will be 25A, so I would go for a 100/50 rating. For 2 x 275Ah, you are looking at 11 hours+ for a 50% charge, so maybe you need more modules too? This would really depend on your daily load. To maintain the battery, you should be looking at replacing your daily load in about 2 - 3 hours of sunshine, so you get some float time in at least once a week.
