Generally, when I am not in a hurry to charge my deep cycle batteries (most of the time), I set the charger at 2 amps (versus 6 amps).  However, is this the best choice (better on my battery)?  Or is it simply a case of 6 or half a dozen of the other-metaphorically speaking?

There's a ton of information floating around regarding this topic.

IMO - it pays to have 'a decent level of working knowledge' on the subject.

It can save one some time, $$$ & effort in the long run.

Here some basic info ~ 

https://www.westmarine.com/WestAdvisor/Selecting-a-Battery-Charger

A-Jay

 

Lots of information...and unfortunately, much of it is conflicting...search BR for posts by @Way2slow with 'charger'.....your level of knowledge will skyrocket

 

https://www.bassresource.com/bass-fishing-forums/search/?&q=charger&author=way2slow

Start with 10 amp then go to 2 amp for batteries that have been drained pretty good. Maybe start with 2 amp if they were only lightly drained. If you only have up to 6 amp option I would start with that, then switch to 2 amp after it has been charging for a while

I think it's more important to have the correct charger, rather than the charge rate. My experience with this is I was using a standard automotive, single stage, typical battery charger and my TM batteries weren't lasting as long as I thought they should on the water. After a lot of homework, I learned that deep cycle batteries can benefit from a true marine deep cycle charger. I thought it was wichcraft but I ended up buying a Promariner Prosport marine charger and my batteries have doubled in their capacity. The same, identical batteries; not new ones of the same brand but the same actual bateries that were failing before, now outlast my days on the water with just a change to the correct charger. These chargers use multi-stage charging where the charger fully charges the battery, then automatically ups the voltage to over 14v for a designated time, then back down to a maintain mode. This process cleans sulfate off the plates; exposing more surface area of the plate to generate battery power.

 

If you trickle charge with 3 amps a discharged deep cycle marine battery it may ruin it.

You want to charge deep cycle marine batteries with 10 to 15 amps until fully charge, then you can trickle charge to maintain 13+ volts.

Lots of reason why this happens, go online.

Tom