Noco G3500 is a great bang for the buck, both 6v/12v charge settings with 3.5 amp output, but charges faster than most in that rating. Also has a 0.9A output for small batteries. It's about $60 bucks online at amazon. Extremely safe and smart microprocessor controlled chargers.
The Noco G7200 is the better product for a different person, with 12v/24v settings, but it's the smallest model they make with the advance desulfation mode. It's about $97 bucks.
The G3500 has desulfation mode, just not as advanced for 12v batteries as the G7200.
If i needed the 6v mode i'd get the G3500. Both are on my next charger to buy list.