Battery Charger

[Bernius1]

Supposedly, batteries last longer if 'ping' charged (Delco). To that end, I re-charged a 1.5V watch battery with a 7.5V wall wart, 3-sec. on, 10-sec. cool down. It lasted about 2-weeks, on 10-min. of charge time.
So, say ; 12V batt., down to 10V , charging off 20V supply; can an op-amp/comparator sense the 10V/12V differential and PWM the charging pulse to avoid *KA-BOOM** ? If so, any battery 1.5V to 12V could charge off 15V, as long as the upper charge limit is provided. No??