Tips for Driving on a Dead 12V Starter Battery (Jump Started)

The 12V battery is not used to start the car - the high-voltage (hybrid) battery does that. The 12V battery is only used for the onboard computers so you should not have any problem as long as it can hold some sort of charge.

 

If they have choices, ask that they use a jump start pack.
They have limited power and usually polarity checking so they cannot reverse the cables.

Their other choice tends to be super sized jumper cables, which, if they are attached wrong even for a moment, can do $4000 of damage. In general they do not do it wrong, but it is painful when they do.

 

Maybe. Probably.

It probably would be better to borrow a battery charger from a friend or neighbor and leave it connected overnight.
If it won't start and keep running after that, it won't make the trip to the dealer either......probably.

ALSO......AAA offers "battery replacement service" in many areas.
In the end having them bring a new battery out might not cost any more than one from the dealer.

 

I'd clarify that to say that the 12V battery boots up the computer and ignition systems, but not any starter motor. Once those computers give the OK to connect the high voltage battery, the various high voltage systems spin a motor-generator that cranks up the gasoline engine.

Once the car is 'Ready', the computers are all powered via a high voltage -> 12V inverter, so the 12V battery doesn't even need to remain present.

 

BUT once the AGM battery gets so low it needs jump starting, it has generally been damaged by the low charge level and needs to be replaced for dependability.

 

Just don't turn off the car and you'll be fine. The 12 volt battery is just along for the ride once the car is in "ready" mode, engine running or not.

Maybe pick up a jump pack, read up in Owner's Manual how to hook it up. Be careful with hook up though: jump point is in the under-the-hood fuse box, and don't reverse the leads.

 

That might be true for (some models) of the Prius but it is NOT true for all cars.
Some charging systems are designed to detect the absence of a battery and shut down.

 

Of course not. The vast majority of cars don't have a high voltage battery and HV->12V inverter at all, nor even a 'Ready' mode. These Prius-specific things are essential to my comment.

 

Not really. How they are engineered is what is important.

The systems in a Prius very well could be programmed to shut down the entire 12 V system if it doesn't detect a working battery being present. Some of the alternator/regulator systems would tend to spike high voltages without a sufficient load (battery). There are various ways to prevent that; one is to kill the alternator output if it occurs.

Since the Prius doesn't do that, lets hope that it's charging system is able to control the voltage without a battery to help filter.

 

I'm pretty sure the Prius is fine to drive with a dead-as-a-doornail battery. That was actually the case with our first drive of ours: it had been sitting for 15 months, and the bozos at Open Road Toyota Port Moody had "warmed it up for us" when we arrived for a test drive. It drove fine, we got back, parked and shut it off, went in and closed the deal.

There was some discussion as to how many km's were on the odo, so we went back out to start up just to check, and it was still completely dead, couldn't even boot up the display.

 

But being "dead" might be different than being missing.......depending on exactly what fault the battery has.

 

I don't claim to know the answer but a dead battery is not necessarily a bad battery, but a bad battery that will not charge may be a problem especially if you can't charge it up to a very minimum voltage, whatever that is.
I am thinking of a dead cell for an example.

 

The AGM batteries used in Gen 2 & Gen 3 Prius cars do not handle deep discharge well.
Your Gen 4 with a regular lead-acid battery may fare better.

 

And it might not too.

An AGM battery is MUCH less likely to sulfate and that is what kills a battery that is chronically left in a discharged state.

 

I left something on that drained the battery down in my 2008 Prius a couple of times but don't remember if it was really dead or just too low to start the car. At that time I dind't have the right battery charger for an AGM battery but it charged it back up and had no problems with it after that. When the battery got old the MFD started acting weird so I just went ahead and replaced the original battery with an Optima Yellow Top. I wasn't in love with Optima and had no opinion one way or the other and it worked until I traded the car in last November. The only reason I installed the Optima was because it was a good deal on eBay.

I don't mess around with batteries anymore, my wife gives me too much grief when I do.

 

No need to just "lets hope" when multiple previous posters have already described their experiences here. Just need to go back to find and re-read them.

And the Prius does not have an alternator at all.

 

A special charger is NOT needed for automotive AGM batteries.

 

I remember one or two of those posts....vaguely.
I don't remember anybody monitoring the voltage on the 12 V system while the battey was absent though.

I never said that any Prius has/had an alternator, but my wording could have been better.