Battery alchemy?

Wifes 2012 Grand Caravan starts to crank slow, been doing that for about 2 weeks. Well today, no go. Half a crank and then the ticks...Its a 3 year battery (2 months left) but we got it with the van and Advance Auto wont honor the manufacturer 3y warranty without a receipt, its a 'non transfer' warranty. Bummer. So im poking around while its on the charger, drawing 2A only (guy said it was good, just a little low on charge which was BS as it wouldnt even crank the van) and I pop the vent cap and find the #1 cell almost empty! So I check the other full cells with my hydrometer and they all test green, but the small bit of acid in the #1 cell wasnt enough to float the needle so I took a little out of each cell and filled the #1, and with all that good acid from the other cells, it still measured 'red' bad. I had some acid from a motorcycle battery so I added it but that cell is still red. Will charging the battery bring that acid back to spec, do I drain that bad cell and add distilled water? I dont know how distilled water turns to acid in a battery....Darn battery is $180 if I need to replace it....I grab the 5 year old reman battery out of the beater mazda and it kicks the van right over. Safe for now, will slow charge the bad battery overnight.