Not Using Car for Three Months

While a slightly higher voltage is better, maybe regular 12 volt charging voltage will be sufficient? I'm out of my depth though.

 

About 25% bad reviews and they have how to repair a problem TWICE in the write up. I would pass on this unit.

 

I'm liking @bisco's jump pack suggestion as good as anything. The stumbling block is the rear hatch latch requiring 12 volts. So if you hook up a jump pack at a more convenient connection point, not to start the car, just to supply 12 volt, then you can pop the hatch.

In my case, that'd mean laying a full-sized jump pack flat in the driver's foot well, running a "memory saver" cable from the jump pack to the obd port.

 

Then he still has to reconnect the battery after a long flight perhaps in the cold, dark, rain. With his solar panel solution all he does is get in, disconnect and move the solar panel and drive.

 

Solar panel is a great idea if sized properly, is safe from vandalism, is in full sun, and it isn’t cloudy

 

If you go with the solar trickle charge make sure you have confirmed/tested the electronics that control it are smart enough to prevent battery discharge at night. Cheap solar chargers sometimes don't have this...

Also hybridautomotive.com sells a harness and charger for your hybrid battery pack and a full charge and balance would be wise to do before leaving it unattended for a few months.

At the same time, there was a recent post on here from a truck driver who bought a used Gen2 Prius, let it sit for an entire year and pretty much didn't have much a problem with it. So maybe all the this extra effort to care for your care isn't really worth it?

 

Maybe too dour? Great idea if it works, rain-or-shine? I believe it's typically within the cabin too.

@MSantos used one, on a Civic hybrid with extra loading: he'd installed a system that put a slight charge on the entire car body all the time, suppose to reduce rusting.

Guide: Installing a solar panel on the HCH-II (step-by-step) | CleanMPG

He shares some math, on what's required. And again, his Civic had higher background loading, with the rust prevention system.

 

Yeah, I’d just stick with a jump pack, great for travellers

 

A bit of info on solar panels for 12 volt maintaining:

Everything You Need to Know About Solar Chargers | BatteryStuff

 

So have you had problems before or do you disconnect the battery so you won’t have a problem?

If the doors are closed the dome lights draw zero power. What does draw power are the computers, radio, clock. Mostly to maintain memory in those components.

 

Jump packs are like the disconnected 12 volt in your car, their voltage should stay fairly stable. I use a Clore JNC660, it's old-school, has fairly common compact AGM 12 volt battery inside. And the manufacturer recommends to charge it up every 3 months or so. There's also very compact lithium ion jump packs nowadays.

It would be no problem leaving it in the car, obviously not in the hatch area, lol. Under a front seat would maybe be good?

 

Ok, now I see. I noticed you are in the U.K. The solar index is lower than many places there. Will you be getting a larger solar panel to compensate?

 

That one....what ??
Totally unnecessary to get a "special" charger for AGM, if that is what you are talking about.

Charging to 95% instead of 100 is not significant in most common applications.

 

NO. Healthy batteries do NOT lose their charge when just sitting there not doing anything.
That includes your car.
Your initial trouble has lead you to draw some invalid conclusions.

 

I suggest that the OP can easily disconnect the 12V battery by removing the 10 mm nut that secures the battery cable to the dedicated positive jump start terminal. He will need a socket wrench for the nut and long nose pliers to pull the cable off the threaded stud.

 

Disconnecting the battery is not his problem. He normally does that. Crawling into the back of the car to open the rear hatch in the dark, cold, rain after a 10 hour flight is his problem.

 

Has anyone actually measured the paracidic draw on a Prius with the smart key turned on and off?

 

Yes, hence I suggested an alternate way to disconnect the battery which will take about 2 minutes and no crawling.