I still have 6 volt in my 1955 IH 300U, battery is about 7 years old and still going, Napa brand. Tractor will sit for 2 - 3 weeks sometimes.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy