In 2007 I bought a schumacher sc2500a. 2/12/25 amp settings.
I noticed quickly that it could easily take the battery well above 16 vlts and the battery would be fizzing up storm. it would not Always do this though, sometimes it would attain mid 14v range, hold it for a short while, then revert to float voltage, and throw the green light.
Unfortunately for the schumacher I Own a temperature compensated hydrometer, and that green light indicated only that the charger quit too early, that the battery was still far from being fully charged.
I found this Schumacher to be totally unreliable as sometimes it would blast the battery well past a safe voltage, pumping 12+ amps and forcing the voltage up into the mid 16v range, and the next time it would stop charging when the battery was only ~92% charged, and I could not get it to actually fully charge the battery, unless i would unplug the charger, load the battery to reduce its voltage, then restart the charger, multiple times.
92% charged is more than good enough to allow even a sulfated capacity compromised battery to start a car.
Do not delude yourself into thinking that any green light full charge indicator means the battery is actually fully charged. Perhaps charged enough, but the lead acid battery lasts longest when it is truly fully charged, often, and those cycling batteries deeper will get more than 2x the longevity by charging to 100%, as opposed to 95%.
I now use a Adjustable voltage power supply capable of providing 40 amps to achieve any voltage between 13.12 and 19.23 volts, and I use an Ammeter or hydrometer to determine just how long 14.4 to 14.7v is to be held, and thistime varies widely, depending n the battery, its size/ health/age/ temperature, and almost NO automatic smart charger accounts for any of these variables, and is simply guessing when to end the higher voltage absorption stage.
"smart' chargers are largely marketing BS, but if a green light gives the consumer warm and fuzzies, then so be it.
Most are certainly more than good enough for intermittent garage duty, but someone actually cycling a battery deeper regularly will not be well served by these garage chargers, as they will almost never be able to truly fully charge the battery, and as such the battery will lose capacity much much faster.
My Sc2500a still works, but its voltage display and all the LEDS no longer work. but its voltage display was always more than 0.35v off. I have a wattmeter on the output leads to see just what the charger is trying to accomplish, but I do not trust it to leave it unattended on any battery I care about. So y automatic smart vharger is not to be trusted, and my manual charging soure, the adjustable voltage power supply, which needs to be turned down or removed once the battery is full, is a million times better and more reliable. Yes there is a dnager of overcharging the battery by leaving it at too high a voltage for too long, but I equate remembering to turn it down or off to driving, saying Gee I hope I can remember I am supposed to stop at stop signs and redlights when I reach one