If I'm going to be using a boat about once a month, and storing it about 180 miles away from me at the lake, how would I keep the batteries maintained at peak power. It will have a cranking battery, and two 12 volt batteries for the trolling motor. I was thinking of buying a 3 bank tender and bringing the batteries home with me after using the boat and putting them on the tender. Is this correct? The boat does not have an on board charger. Any other ideas out there? Thanks.

I can think of only one satisfactory (to me) solution: spring for an on board 3 bank charger that goes into maintainer mode once a battery is fully charged. That works assuming you have elec service at the storage. A tender alone won't do the job. The trolling motor batteries should be charged after each use. A tender will not "charge" a battery, it just maintains existing charge level. I sure would not want to pull out the batteries after each trip, then have to reinstall for the next trip. I would end up just not going fishing as often.

I understood that a battery tender will also charge a battery (ableit at a very low amperage/voltage). Is this not correct?

Is the tender you are thinking of getting actually a charger with automatic maintainer mode? If so, what about using it at your storage place? That less cost than an on board 3 bank charger.

I just did a quick search, and Deltran makes a tender that does charge then go into maintenance mode. Not cheap, though. Maybe there are others that will do the job but not as expensive.

Thats the exact maker I was looking at when I started researching battery tenders. The deltran model seems to get very good reviews also. I would think on on-board charger will also go into maintenance mode when the batteries are fully charged, correct?

Yes, a good on board charger does have an automatic maintenance mode. Check BPS for example - MinnKota 3 bank for $290. Description gives details about features.