I was having this issue with a group 31 that Inrterstate insisted was still perfect (under warranty). I bought a $50 jump pack at Walmart that is about the size of a paperback book. It is rechargeable and has started the boat 7 or 8 times now. I replaced the interstate battery with an Optima and am no longer having issues, but you can bet that jump pack will stay charged and in a zip-lock bag in the boat from now on. I know that the Interstate is faulty, but hooking it to a tester after it has been charging is not the same as it needing to work all day on the water.

I had an Interstate that I had lost all confidence in. The guys at the shop looked me in the eye and told me it checked good. Long time shop, I believed them. I told the shop manager I had lost confidence through repeated failures and please just put a new one in. She did. She would not take my money. Weeks later I checked in and she told me Interetate replaced the battery. I told her my truck was fixed. Win. Win. Win. I'm an Interstate man.

I've had bad luck with all of the Interstates I've tried in recent years. Before anyone questions my habits, yes, I'm a stickler for proper maintenance and charging. That didn't help the interstates I had....

are you unhooking the graphs in storage. The "poles" and graphs can draw power when your not using them

I have two 12s and running the aerator on auto all day without running much (less than 5 mins after you reach your original starting spot) will definitely run down your cranking battery. Fortunately I have room to add a 5th battery and wired it parallel with my cranking battery. ZERO problems since then. I realize you don't have room to do that but maybe this will help someone else out.

You should install a battery switch so that you can run from ONE battery while keeping the other battery isolated - in pristine reserve for when you need it. By hard-wiring them in parallel, if one of the two begins to fail, it WILL drag the other battery down, consuming its energy. Then, at the end of the day when you want to go in, you'll have TWO batteries that neither of which will crank your outboard. Using a battery switch and selecting #2 before attempting a start will guarantee a fresh battery for the start-up. If you do this, NEVER switch between batteries while the engine is running. (Outboard manufacturers don't like this.)

Over time, one of the two will begin to fail. With an isolation switch, the other battery will still be in good enough condition to just replace the one battery. If the bad battery has had enough time, it will make sure you need TWO new batteries....

This is sound engineering advice - not 3rd party hearsay.