Having owned a number of battery chargers for motorcycles I've been a long term fan of the Deltran "Battery Tender". I keep both 6 and 12 volt configurations. These are on any bike that has a battery in it and it's how I've been able to get a factory Harley battery to last more than 8 years. As for charger experience I've had Schumachers, Sears and also keep a “full-house” stand alone roll around charger for multiple big-batteries like our farm tractors and tractor-trucks.

Recently, a friend gave me a very nice AGM battery as a belated Christmas present for the '74 911. Since everyone knows my cars are driven a lot I wanted to keep it up to snuff and attached a "Battery Tender Junior" to it. Unfortunately, due to it's output (750 ma), it wasn't able to establish any sort of charge on the battery in a reasonable timeframe. The Porsche accessories catalog lists a charger with "PORSCHE" inscribed on the cover which I've had on the GT3 for a while and have been very pleased with it. It uses a back feed hook up through the cigarette lighter which is pretty convenient. So I went hunting. Further reading on Porsche and other car related websites revealed the name "CTEK". The brand (designed in Switzerland) has good feedback and when I looked them up it's apparent that other auto manufacturers like them too. The conclusion from those who wrote these snippets is that the CTEK is the same charger. It is, however, available in multiple configurations.

I purchased a CTEK (MURS 4.3) from Amazon.com. After only a brief period connected it was apparent that it was bringing the battery to full capacity pretty effortlessly. It soon went "Green" and is now in the stand by mode. Amazon charges $68.49 for this model and will ship "Prime" if you are a subscriber.

http://www.amazon.com/CTEK-56-864-MU...attery+charger

I will continue to use Deltran Battery Tenders but this is another good option.

Tom