12V surprise

Sounds like the ECU settings were lost, and the car needed to relearn the best settings for fuel, climate, and driving style.

 

apparently OEM 12v battery lasting 5+ yrs. Car bought in 2019 Sept. Just had it checked 5yrs/3 mo later, still has 82%. just hope it just doesn't suddenly collapse.

 

The danger of having an exposed positive and negative connection near your battery terminals would make this a high risk proposition. Also, there could be a danger of arcing when connecting the jumpered connectors up to the new batteries.

Having had to replace the display unit in my 2018 Prime, I am EXTREMELY careful with anything to do with the battery. FYI - if you reverse the leads on your battery charger or cables, one of the very first things to blow out is probably going to be the display unit. According to Toyota, there are fuses inside the display unit that are replaceable but I wouldn't count on it. My issue was my head unit just died for no apparent reason. Toyota quoted me $9k (!!!!) for a replacement display unit and about $1k in labor. Luckily I found an independent Toyota Master Mechanic who swapped in a used unit that cost me about $1200 and about $500 for labor.

 

Any prelim. probs with head before failure?

 

I'd like to ask whether one particular option works on a Prime. First let's get the others out of the way.

Option 1: don't let the 12V battery discharge in the first place.
PRO: improves battery life, doesn't cost anything, and is widely considered easy to do.
CON: it would be easier to do if I lived alone.

Option 2: Keep a jump start pack in the glove box
PRO: You can jump other people's cars.
CON: By the time you use it, the 12V will already have been damaged by the deep discharge.

Option 3, the one I'm wondering about: install a "priority start"/"battery protector" unit.
These normally are transparent but when a 12V gets too low they disconnect it to prevent further discharge. Then when you get out to the car and realize the situation, you can push a button to reconnect the 12V while you start the car.
PRO: saves battery life and prevents problems.
CON: You have to reset everything, and I have no clue whether they work in a Prime. Is that override switch going to be compatible with the zoo of electronics under the hood? At least there seems to be room to install one, unlike my other Prius, a Gen 2 with the tight trunk compartment.

Has anyone installed one and been happy? If so what brand?

 

Option 4: Get a Battery Tender installed to keep a trickle charge on the 12 volt. You have to keep it plugged in all the time, so if it's not convenient to an outlet, it won't work for you But otherwise it is a simple, trouble free solution.

 

That’s my approach. I replace the stock battery in September of 2015, with an Optima YellowTop (not the best option in hindsight, but working fine).

The car is garage parked, currently seeing about 3k kms use per year, and invariably on a charger, using a quick-connect for convenience. Still testing well, CCA well above spec, and at-rest voltage 12.8~12.9.

 

Thought that was a pert of option 1. Keeping it plugged in falls under the con.

 

With the most recent flat battery (the Gen2), it was connected to a Battery Tender. The Battery Tender could have handled the regular turned-off current draw but with an interior light left on for three weeks, it could not keep up.

Well, then, Option 1A, a higher capacity Battery Tender.

Is there even a way to install undervoltage protection in a Gen2? That's one cramped battery compartment. Would it work if so?

Starting to wonder if we should just lend the cars to neighbors when we're on long trips and let the car handle maintaining the charge.

 

It invokes the option 3 con, but simply disconnecting the battery is an option when away for long. Can even keep the battery on the minder.

 

Reasonable option. Con, it's a fair amount of work to get all our junk out of the trunk, find a place to put it, and get to the battery to disconnect/reconnect it.

For a little extra work, I could turn off the smart key system for the duration of the vacation. That would reduce current draw.