I bought a supposed high quality smart charger and it crapped out the third time i used it. I have a 50 year old gas station booster/charger that is going strong. I would like a nice smart charger but one that won't take a dump after a few uses. Price not really an issue.
Old chargers that allowed you to set both the voltage & current are done by making a trasnsformer with multiple secondary coils and a very complicated switch to bring individual or multiple coils into the circuit .
Tis is why they weigh a ton, got to be 40 lbs of copper wire in them.
Modern chargers use power transistors that are by nature very frail .
Most are glued onto a heat sink with a conductive glue usually made with silver or gold so is very $$$$$$
It also is not particularly strong mechanically so dropping the charger can crack the glue causing the transistors to cook in no time flat.
Because they all use a feed back loop off the actual battery to adjust the charge it is very difficult to protect the circuits from reverse wiring and the diodes used are generally not up to the job & way too slow .
The ones with a reverse polarity relay & breaker are the best but expect to pay big dollars for them ,
So stick to you old mechanics charger and if you are worried about cooking a battery then use one of those timer switches to shut it off after the hour you think the battery will need , about 1.5 x the amp hour rating is usually a good place to start .
I use a couple of timers to keep the motorcycle batteries charged.
15 miutes at full power once a week is a lot better for the battery than a 24/7 trickle