It's all about what the batteries want, not what people want or battery recharging device manufacturer's want.
"Is he hungry?"
"Dunno. Is he reading? What color socks is he wearing? What kind of car does he drive?"
;) A good metering system can tell when a battery is laying back with a satisfied smile on its face or sitting there with its tongue hanging out. But it cannot see what's in its stomach.
When you suspect a converter or charger reading is growing a long wooden nose, you have to verify it with a hydrometer or play the part of a pipe organist and start tweaking the voltage. Like petting a strange dog. If he wags his tail, he's happy. If he takes your arm off, then you guessed wrong...
Amp hour meters need periodic re-zero-ing and with a sealed battery that means twirling knobs and poking a stick at the battery. Wet batteries are easier.
Two airplane pilot angels in heaven...
"For the life of me, the altimeter said five hundred feet"
