Extending run time on new batteries (wired parallel)?

This has probably been asked here 100 times before, but I’m new to the forum and new to running batteries in parallel. I have a 55lb. thrust, 12 volt trolling motor on my 2 man boat and have always run a 100 amp hour battery, but due to my cancer I don’t want to be lugging 60-70 lbs. in and out of the boat each trip. Could I get the approximate run time from two 55 amp hour or even three 35 amp hour batteries wired in parallel? I would want to wire them parallel rather than in a series to keep them in a 12 volt configuration, correct? Also, if you guys and gals know of any good deals let me know. I’m cheap and only want to spend maybe $60-$100 per battery, so I know my options will be few. Has anyone owned the Mighty Max 55 amp hour or 35 amp hour batteries? I’ve heard both positive and negative reviews. I worry that two 35 amp hour batteries wouldn’t give me much run time, maybe not even three would be enough, let me know what you think.

Your theory is correct. Batteries hooked up in parallel you add the amp hours, same voltage. So technically (2) 50 amp hour batteries in parallel should equal (1) 100 amp hour battery.

Real life, my experience, as you add more batteries, it is not 100% equivalent. I think as batteries start loosing their life, in a parallel situation, it follows the worse battery in the group, so degrades faster.

But that said, it should work as you describe.

Have you considered an onboard charger so you dont have to take the batteries out of the boat (I’m assuming your doing that to charge them, if not ignore this LOL)

It works, just make sure they are both the same age, brand, and size. Also keep a close eye on the batteries, better yet disconnect them from each other between uses; if one battery goes bad it will take the other one with it if allowed to suck it dead.

I had the same configuration about 15 years ago. Boat had 12V motor, enough power for light hull, but if I fished all day, battery life was too short. Installed two batteries in parallel, also installed on board charger, never had to remove batteries again.

To avoid dealing with paralleling them, there are switches out there that you wire each battery to, run one till it’s dead or close, then turn the switch and it switches you to the other battery. Then you don’t have to worry about 1 battery going bad and dragging the other one with it.

I think this video goes over it in pretty nice detail. He does it for a different reason, but it should work the same for a trolling motor