Adding water dilutes the sulfuric acid mix which in turn slows the chemical reaction.
So yes it is possible.
But what is more likely, is your reliance on the well marketed 22.7 stage automatic charger to do the job at which it claims to be proficient, which is fully charging a battery.
Automatic chargers are designed to NOT overcharge a battery. Since all batteries vary slightly in what it takes to fully charge them, no one size fits all smart charger is going to do the job it claims it can do.
Even if it has flooded/AGM/Deep cycle/Gel settings, these algorithms are still cautious and tentative and still undercharge the battery 9 times out of 10. The battery which was only discharged to 90% needs much different charging parameters than the one which was drained dead and jumpstarted in a parking lot and driven 10 miles home.
Also batteries as they age tend to need higher voltages for longer to fully charge, and Automatic chargers do not account for this.
IF the charger has a Float/maintenance mode, leaving it plugged in for a long time after the full charge indicator initially alights will eventually max out the specific gravity. Such a battery might take 0.15 amps to maintain 13.1 volts, but this same battery might require 7 amps to be brought upto 14.5v. If it requires 7 amps to reach and hold 14.5 volts, it is far from fully charged.
Get a turkey baster style glass hydrometer like the OTC 4619, and it will reveal your Alpha and Omega smart charger, is actually afraid to bring the battery to full charge.
A trick with automatic smart chargers is to remove the charger from the battery after it shows the green full charge indicator, turn on the lights to drop battery voltage to 12.6 or less, turn off the lights, and then restart the charger.
I had to do this 10 times with a Schumacher charger before Specific gravity rose above 1.275 on a friend's battery. He refused to believe that his 80$ charger's green light was a liar, and I bought the glass hydrometer for him just to prove the point that it was.
For my own heavily cycled batteries, I use an adjustable voltage 40 amp power supply and set it to ~14.7v, and let it go for as long as it takes for the SG to get within .005 of my observed maximum. And this always takes longer than one would expect, and sometimes voltages upto 16V are needed to do the job.
After I refill a battery, the voltage under load is always lower, and it appears as if filling has hurt the battery, and as the electrolyte level drops the voltage seems to rally under the same discharge.
I tend to keep them more full than not, as weaker electrolyte is less abusive to the plates, but achieving a true full charge is a little more difficult with the weaker acid solution.
The Hydrometer is a wet/flooded lead acid battery polygraph. Open circuit rested voltage only tells a small fraction of the battery condition and state of charge. Even less reliable is the green full charge indicator on smart chargers.
AGm batteries require either an amp hour counter, or for amperage to hold absorption voltage to fall below a certain number.
When my Northstar AGM battery takes less than 0.4amps to hold 14.7v at 77F, I consider it fully charged and only then disconnect my power supply.
