OPtimates are first class but pricey. My very old one is still good byt 12v only. I also have a couple of Lidl smart chargers. very good and will automaticaly detect 6/12v. Some smart chargers won't start charging a dead battery because they can't detect a voltage. No problem to give a dead bike battery a 10 min. blast with a car charger before connecting the smart unit. Sometimes works.