How much driving to maintain 12v?

That is more than enough to keep it running optimal...

 

Another concern with that kind of use will be corrosion in the cylinders and exhaust. A by-product of combustion is water, and if the engine doesn't get hot enough, it will stay wet and corrode faster, from the inside out. The crankcase oil will foul quicker. Frequent short trips are bad for any car. (Consider a bicycle for those?) The Prius has an on-board thermal storage tank that will help with cold starts, at least, but you won't be getting up to full operating temp.

The Prius 12V does not crank the engine, but boots up the computers and runs the accessories. One long weekly drive should be enough to keep a healthy battery charged. But if that battery is more than four years old, consider getting a new one. Also look on this site for the steps to read the battery voltage without tools using the dash display (MFD), and keep an eye on it. Your use of accessories like A/C fan, interior and exterior lights, windows, etc, will affect the charge.

 

If your mpg's start going downhill all of the sudden without any other explanation, that's a good sign that your 12v is shot or due for replacement.

 

1. The typical weekday usage is going to be very hard on the 12V battery and the engine, for that matter. That really short driving is bad for the engine as water condensation will build up in the crankcase.
2. The Saturday drive is helpful but a 20 mile drive by itself is not going to be sufficient to keep the 12V battery charged. 200 miles is starting to be long enough.
3. It is not necessary to drive the car "on the freeway" just to charge the 12V battery. What is important is how long the car is READY, not how fast the car is moving.
4. You can have the car sitting in your driveway, in READY, and that will charge the battery at the same rate as you driving 70 mph on the freeway.
5. Hence, if you do not wish to use a battery charger, make the Prius READY and let it sit there 4 hours or more. Make sure the fuel tank has sufficient fuel so that you do not run out while the car is sitting around. I suggest you do that once a week.

 

This mirrors much of our family's driving and a major reason I went with a plug-in EV years ago. Anyway on our '06, I have a connector for a battery trickle charger (aka battery tender) permanently hooked up to the 12v and the weather resistant plug hangs outside the car for easy access. I plug it in overnight or longer about once a week (usually weekends) to keep it topped off. There's also the continual drain of the SKS unless you turn that off.

 

i used to drive 14 miles a day and never had a problem. 7 out in the morning, and 7 back at night. can't speak for how much less would not be detrimental.

 

put a smart charger on it once a week under the hood, or permanent connection in the hatch, problem solved. (if the golf trick doesn't work)

 

I owned a Gen 2 and my scangauge only showed 13.8 volts when ready, the same scangauge shows 14.4 in my v any time it is ready. (The Prius has no 12 volt alternator, so engine speed is not a concern)

I think Toyota realized they were not charging the 12 volt enough.

I suspect that your week end mileage is enough, but I am prescribing a weekly drive to a gold course 30 miles each way "just in case".

Coyote Hills Golf Course E Bastanchury Rd seems nice

 

Very easy DIY. Hook a smart charger, let it run to a complete cycle, say every six months, would be like taking multi-vitamins when you think you might be missing something.

We're kinda borderline with usage, not as bad you though. The car will sometimes sit 2-4 days, but our runs are longer, almost seek them out, because I know it's good for battery, engine, and all.

 

Keep it 4 amp or under, ok for use with AGM batteries (preferably a special AGM setting is good, charges at higher voltage), and a smart charger: goes through charging stages, monitors as it goes.

CTEK is a good name, what I've been using (a 3300 and 4.3) not that cheap though. There's a lot available.

 

about 70 bucks on amazon.

 

That routine will be tough on the battery. To see how tough at the end of the week before your long drive first thing in the am before you start the car get a dc voltmeter and check the front underhood battery jump points and see what the 12 v battery reads.

I'm thinking 12.1 if the battery is healthy.

 

yes, if you open the user manual, it says there is a 3 amp setting for wet batteries.

 

That's the first one I got, and actually a little easier to use/understand than the 4.3. Not sure where you're seeing 7 amp, believe it's 3.3 amp. I would use the regular (automobile symbol) charging mode for rectangular AGM, and the higher mode (snowflake symbol) if it's a spiral wound AGM, like an Optima "6 pack" battery.

Once the floodgates are open, there are other toys to consider, lol. A digital multimeter is worthwhile, not just for your car, lots of uses. Also, specific to automotive battery assessment, something like Solar BA5 is good.

 

the amazon link shows 7 amps under technical details. probably the max output, or maybe a misprint?
users manual doesn't show it.