Glenn, Knottyrope brings up a good point when he says that a "new, off the shelf" battery is most likely not fully charged. You can "zap" one with a 10-amp or higher rate for an hour and see the terminal voltage go above 14.5, but that doesn't condition the plate chemistry completely.
"Slow but steady" is what is needed to get below the surface charge on the plates and get good chemical change penetration.
The little Sears charger I use, which is not a day over 45 years old, has three charge rates, a timer, and a built-in voltmeter. The three rates are 10A, 1.5A, and .38A. When the timer turns off, the charger continues at the .38A rate.
When I want to "top off" a battery, I'll start at the 10A rate, and switch down to the 1.5A rate when I see 14.5 volts. Terminal voltage will go down to around 13.5V, and I'll set the timer for 4 hours. With a half-charged battery, the terminal voltage generally goes down some, indicating that the charge current is penetrating into the plates. I'll reset the timer to 8-12 hours if voltage goes down significantly, and go about my other business. A rise above 14.5 volts indicates "near full charge." If voltage is still down after 8-12 hours, I'll let the timer switch off to the 380 ma rate for 12-24 hours, and switch it on to the 1.5A rate for another few hours.
On a big battery, like the group 49 92AH battery used on Mercedes cars, this cycling can go on for several days. Even on those batteries, which are whoppers compared to garden tractor batteries, switching to 10A can show nearly 15 volts, while going back to 1.5A goes back to around 13.5, indicating that the battery is not yet completely charged.
I have swapped notes with a genuine battery design engineer, who confirms my observations that an open battery that doesn't come up above
14.5 volts at a 1-2 amp charge rate either is still accepting a charge or has a cell problem.
Voltage drop while charging at a low rate following a quick higher-rate charge is normal, sez he.