Toyota sent me an email for 25% off genuine Toyota parts. The True Start 12v battery for my Prius would be $154 after the 25% off discount for black Friday. Is that about as good as it gets for a new genuine Prius battery? I have been charging my 12v once every other week. It has no issues at all but I know they are supposed to last 8 years. It's getting to that point and for preventative maintenance, I was thinking about pickup up a new battery. I figure that I can use the current battery for another year and charge up the new battery once a month until I replace it. Should I wait until my battery dies or pick up a new battery?