I use a 1 amp charger for about 8 hours or tad bit longer. Just a guess but could go longer say 12 hours but say 1.5 to 2 amp charger no need to go that long IMO. I once long, long ago made the mistake of just charging up say an older cycle battery with a 10 amp charger for a few hours and fried that battery was boiling inside could hear the acid just bubbling making noises and battery was VERY HOT to the touch, not good.
Last time I sealed the holes after installing acid on new Yuasa battery before charging on my 1 amp charger. What is the negative effect of closing the fill holes BEFORE 1st charge? Is it that big of a deal?
Brand new acid, brand new lead plates, first charge (energizing chemical energy) is the most important one a battery ever gets, and is bubbling away (and creating plenty of gas) on that charge, even at low amps if you do it for the recommended time. You go in your garage or shed right when it's done, you'll smell it.
Even with the vent line, sealing it up for the first charge could result in an explosion. That's why the directions tell you not to plug up before first charge. The Yuasa is called a sealed battery, meaning once that strip plug is stabbed in there tight, it's really never supposed to be removed again. It can be done, but it may leak thereafter.
I had a car battery explode in my face once (at my first gas station job). In 2.5 seconds, I climbed into a big sink backwards and turned both faucets on full on my face, and held my eyes open with my fingers, for a while. No burns at all on me (but my shirt and pants took a hit). Scared the hell out of me.
