What type of charger do I need to charge two 12 volt deep cycle trolling motor batteries at once?

Well, I charge three 12V batteries at once with a 3 bank Dual Pro Charger. I also charge three other 12V batteries at the same time with three separate 12V portable chargers.

If you have your two batteries connected in parallel as several on this site have advised against, then any single 12V charger will charge them both eventually with the highest capacity charger taking the shortest time.

If you use them separately or as a 24V series hookup, then you can do it like I do my 3 battery setups.

You can charge them with a 24V charger if they are connected in series also.

How often do you fish and how are the batteries hooked up?

When Im done fishin I connect my crankin battery and my trolling battery with a homemade set of wires and alligator clips.{sorta like mini jumper cables} I then use a plain ole battery charger on trickle charge overnight. Ive done this for several years with no problem.

I have been doing that for ten years with a single charger or off the truck too. Single charger will work fine if it is a good charger.

I do mine seperately with Battery Tenders