I'm looking for advice about my cranking battery. It's a marine cranking battery that I bought a year ago at O'Reilly's. It shows 860 cranking amps, but last week, during our annual trip to Table Rock, we had to "jump it off" 3 times. It's cranking a Mercury 200 4 stroke, and I was running 2 Lowrance 9" Carbons and one livewell. The alternator registers a 13+ volt output, so it seems to be adequate. Thoughts? Advice?