Also, do you have a battery cutoff switch installed?
Electronic brainboxes on many devices are active even with the device powered off…
Testing the battery load, I could clearly see that even starting with a fully charged battery, there was enough of a load on the battery from all the little brain boxes spinning away in the background that the battery was losing 3-5% of its charge every day. So the boat owner was starting out a half-charged battery or less to begin with.
So yes, a bigger battery may be the answer, but also I’d seriously suggest looking at a cutoff switch for the starter battery.
Yes, for sure – this is one of the main reasons I’m looking to add a second house battery – to keep the starting battery isolated from all those small drains of current. From what I’ve found, either option I posed above (Minnkota Onboard Alternator or the Blue Seas Add-a-Battery) will essentially isolate the starter battery from any drain outside of the outboard. The Blue Seas allows you to select to cut off connections from both batteries so that’s a plus for that system. With the Minnkota system, if the outboard itself had a small draw on the battery when not running, that would still drain the starter battery but nothing in the boat would be drawing any current from the starter battery, even if the Master Power and Auxiliary switches were left on (and I always put both those switches to the off position when done for the day).