Accumate best investment I've ever made. Been using it on my bikes and to date not had to change one single battery. It can do both 12 & 6 V batteries. Came up best a couple of years ago in the "Ride" mag test.
It has enough oomph to even charge and maintain my car battery (although it take a long time).
There is also Optimate (also very good) which has more charging stages but strictly motorbike batteries as it has a lower current delivery and 12V only