2004 Optimax 115 for 72 Seafari 20

[Bushwacker]

One of my 2 batteries has been weak for last year or so and never comes up to more than about 50% of max capacity, I think about 12.4 volts, unloaded. I always run on it and keep the other one in reserve. My E-Tec always lights off within 1 revolution with the weak battery. I think it's started down as low as 12.1-12.2 volts; can't remember exactly, but it's never failed to start.