I entirely agree with Bill's comments but would like to add some about your charger since that will be what keeps your NEW battery from dying early:
1. Though it is a 3 stage charger it does not go over 14V in bulk charge stage and you should really charge at around 14.5V for maximum reduction of the sulfation Bill describes.
2. It has no EQ cycle capability which means that you have no way to "knock off" sulfation after the fact.
Given your use, it is hard to justify an expensive new charger. You may be better off just leaving the charge plugged in full time and topped up with distilled water as Bill suggest.Given your charging system, I don't think you can expect real long life from your battery...but you can certainly avoid killing it as quickly! (g)
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