agree, charge 'em at 10 amps - keep a close eye if it's not automatic shut-off.
you want to recharge your trolling battery soon as you get home after every trip, and recharge both batteries every couple-three weeks between uses...a battery will self-discharge, and any time spent at less than 100% charge will shorten its useful life.
if your "maintenance-free" battery isn't "sealed", you still have to check the water, use only distilled water and only add enough to cover the plates. Check 'em more often in hot weather. Low water and storing in a discharged state are two biggest causes of premature failure.
When you buy a battery get the freshest one on the shelf - no telling how long yours were on the shelf building up sulfation.
overnight 2-amp trickle charge probably won't kill your battery but unless your charger has a "maintain mode" (automatically turns on & off as needed) don't leave it on 24/7, it will overcharge - really bad news if the water boils out.
No reason you shouldn't get 4 or 5 years out of a cranking batt if ya take care of it. Trolling batteries is another story, 2 years maybe 2 1/2, depending on useage.
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"The metric system never really caught on in the states. Unless you count the increasing popularity of the nine millimeter bullet." -- d. barry