I have a RT188 Ranger (alum) w/ 80 lb Ultrex. Just purchased 3 Group 34 AGM Duracell's. 1 for cranking, 2 for Ultrex. Got them home and realized they were smaller than what I had Group 27's. Guess I was under the impression the bigger the number the bigger the battery. Anyway, being an aluminum boat I believe the batteries should run the ultrex all day. Anyone have any experience with these?