I have a 2008 Prius as a second car, which I have driven once a week since my husband passed away in October 2009. Today the battery was dead for the second time. The serviceman at the dealership told me that I would have to drive it about every other day in order for the starter battery to keep a charge. He told me to get a “trickle down” battery charger and keep the car plugged in if I was not going to drive it every other day. My normal practice is to drive it once a week, and that has worked for 1 1/2 years. I had not heard of this before, and I can’t find anything on the internet on this topic. It sure would be a nuisance to have to plug in the battery every time I drive into the garage.
When you drive it, how far do you go? That’s important. If you’re driving it far enough to fully charge, then once a week should be more than fine.
If you do need a trickle charger (not a “trickle down” charger), check if your lighter socket is live when the car is turned off. If so, I’d recommend a charger with a lighter socket plug so that you don’t have to mess with anything under the hood each time.
It may be a bit more complicated. The 12v battery is not the battery that starts the car, it’s the large high voltage battery that starts the car. A trickle charger won’t charge the large battery. The solution is you need to drive it more. Why not sell it?
Also, to add to what Texases said, the 12V battery that turns on the electronics is a really small capacity battery. It doesn’t ‘need’ to be large like conventional cars, because it doesn’t run the ‘starter’. It just powers the electronics until the hybrid system is started up. The hybrid system then runs the car and starts the gas motor if the hybrid system battery gets low.
Being a small capacity battery, it cannot keep a charge as long, even with the small draw the module memory circuits use. Especially now that it is a 3 year old battery. I’m surprised they didn’t offer to replace it. These things don’t last forever.
Sorry for the loss of your husband. At this stage of life, are you sure you need to have a second car? More maintenance, more registration and yearly inspections, more insurance costs, etc. An '08 Prius would sell at a good price as used car prices are high now and that model is in high demand. Then which ever car you keep will get driven enough to keep the battery charged.
If you keep the 2nd car you don’t need to put it on the charger every week. What would work is put it on a “battery tender” charger once a month and leave it connected for several days until you use the car again. With a battery tender charger you really won’t need to drive the car weekly and you can leave the charger connected all the time without harm to the car’s starter battery.