The Battery Tender is good but I swear by the little unit sold by VDC electronics ( www.vdcelectronics.com ) The battery minder not only maintains the battery but it also desulphates it at the same time. I skeptically bought one with the promise that if it did not work as promised - they would refund my money. Three years later they will have to fight me to get it back. I also bought the 6 volt model for my 1930 Chev battery and it still cranks like new 3 years later when I only drive the car for about 10 hours a year. This little unit will maintain and desulphate up to 4 batteries at the same time. My garden tractor battery, my Mercedes battery, my son's Porsche battery and my spare VW battery are all like new after three years with them on this little marvel for 6 months out of the year. I had one battery that was 5 years old and so sulphated - I was going to take it for re-cycling - after 4 months on this baby - it is still working in one of our cars! Some say I am crazy and it is snake oil - my real life experience with it says it works - read their website and decide for yourself. The product is patented so it must work or the Patent office would not have given them one. I have a patent and know that you have to prove your claims to the examiner before they will even consider issuing a patent.I would appreciate hearing from others who have tried it.
Morris