Dead battery twice in two weeks.

How old is the current 12 volt battery?

If you check the jump point under the hood in the morning after the car has been off all night, what does the voltage read?

Replacing the 12 volt isn’t that hard, and Auto Zone or the like have deals on the batteries.

Just make sure the battery has the vent port.

Good luck and happy new year.

 

After you replace the 12V battery, get a CTek 3300 (link here to Amzn, but you may find it cheaper if you look around, just make sure it's the 3300 model for US). This is a 'smart' charger, which means it monitors what it's doing and stops charging when done, then holds the charge as needed, so it can be left attached to the battery indefinitely. It comes with a nice pigtail which you can attach to the battery terminals in the back--as I have mine--or to the jump points under the hood. I just fished the pigtail up into the cargo area from below on extreme right rear. No need to disconnect the battery for charging, and it even has a cold weather setting. Excellent product; I'm in a similar situation to yours, days go by between driving episodes.

Note: I use a good outdoor extension cable for connecting, and there is enough leeway at the rear hatch seal to allow the CTek cable to extend outside the car and still fully close the hatch (gently).

 

The one you tried is NOT a battery maintainer, which is what I'm talking about. It will keep your (new) battery healthy, NOT jump start the car. Please reread my post....

 

That's a fair deal.

Ok, that's not so good. If you're using the car as a daily driver, doing at least 10 miles a day regularly (say 5 or 6 days a week), it should last at least 4~5 years. If it's often shorter trips, and the car regularly sits for multiple days, then you should start thinking about an automatic charger, something along the lines that @Ed Beaty describes.

That's pretty much exactly my situation and solution, except that I'm using the CTEK 4.3. I have a 3.3, that was my go-to charger for years. Keep it in the car as a spare now. I used the supplied quick-connect wire, which is handy if you're going to be hooking up regularly. I connected at the under-the-hood fuse box positive terminal, which is a little tricky to access. See @NutzAboutBolts video #23 here:

Nutz About Bolts Prius Maintenance Videos | PriusChat

You connect the quick-connect's positive lead there, and the negative to grounded bare metal. I went with one of the bolts on the Inverter coolant reservoir's support bracket IIRC, because it was right there.

When connecting, always make the connection to wall current last, and disconnect it first. And keep an eye on the status lights. And read the manual, lol.

Also, I found it was really tight fit installing the positive lead, needed to strip the (mostly ornamental) plastic shoulder insulation off the pigtail connector, and bend it (carefully) through a right angle, in order to get it fitted and the cover back on.

I left the (capped) quick-connect laying loose in that corner. When I need to use it I pop the hood, connect to the charger, then lower the hood gently, on the wire, just ajar, not fullly closed. This works for in a secure garage, for me.

For outdoor use, you might want to consider running the connector out through the grill. I have a concern with an install like that though: seems like someone could short out your battery if they had a mind to. Best to keep such an install well hidden.

Well, New Year's Day, more'n likely an idle day, I'll go out to the garage and plug it in.

Done. Once plugged in thus, it will run through a charging cycle (takes maybe 4~6 hours), and you can just leave it thus till the next time you need to use the car. There's no danger of overcharging: it runs through a charging cycle (read the manual, to determine optimum schedule, there are options), then subsides to sporadic trickle charging.

 

There's nothing wrong with the CTEK 3300; it actually offers virtually the same functionality as the the 4.3. Common story for me: I'll buy stuff for my son, and it's "Ah Dad, I'm never going to use this; You keep it."

Which is mainly why I have the 4.3. The one extra it has is the ability to do a desulphate cycle, if I'm not mistaken. I don't believe the 3300 has that. I've used that once, but normally just use regular automotive charging cycle, and since I have an Optima Yellow Top, I follow the manual recommendation and use the the "snowflake" option, which is slightly higher charging voltage IIRC.

But yeah either is good. The 3300 is 3.3 amps, and the 4.3 is (you guessed it) 4.3 amps. I'd suspect the 4.3 gets through the charge cycle faster, but doesn't seem to be a lot of difference.

 

IMO that lithium jumper should have worked. I have one. I have not tried it on a Prius, have not needed to. I have used it on a 4-cyl Honda with the battery entirely disconnected and it started the car. I've also used it on a Toyota Highlander with a dead battery and it started it right up.

Strongly suspect your current 12v is shot. Likely has a shorted cell. When the rest are fully charged it....barely.....starts the car. When it sits too long the voltage plummets until it no longer has enough to work. This is typical behavior for a dying battery.

With your driving habits I also recommend a battery maintainer. Seems a number of EV and Hybrid cars are poor at taking good care of the 12v system. I use on on my Nissan Leaf regularly.

 

Erratum: Looking more closely, it appears that I have the CTEK MUS 4.3 as well. Somehow, I got '3300' stuck in my head (I blame Leisk....). At any rate, it's a great piece of gear and works well (is working right this very minute, in fact).

 

If you don't have one it's also worth picking up a digital voltmeter. If you have Harborfreight near they are pretty cheap. You don't need to spend a lot on this as measuring 12v Pb is not delicate electronic work. You simply want to see it over 12v for sure. At 12v it's actually getting a bit dicey. It's best if it's something like 12.5-14v. My 4 year old battery shows ~13.5v after a fresh topping charge.

 

What is your tank-ly MPGs?

 

I’m curious... I’ve had the same 12V battery in my car since new; April 2012. Granted, I don’t have cold winter weather. When the battery dies, I’ll replace it. But why the rush to get a battery maintainer? Original battery lasts five or six years without a maintained so the replacement should as well... unless you don’t drive the car often, etc.

 

Agree. Most 12V car batteries life span are 3 to 5 years w/o maintenance if vehicle recharging system is working properly. If you're in need of constant recharge with car off, you either are experiencing parasitic drain or battery needs to be replaced. Once you buy a new battery that holds charge up to 12.7v, there's no need to buy charge unit unless you drive it once every 2 weeks.

 

Hmm..I'm curious about this as well..

Seems to me the first step would be to replace the 12 volt. Then in the future if you want to go the battery maintainer route, it always exists.

But if the 12 volt is failing, it just needs to be replaced.

As far as could something be draining it?
I kind of doubt it.
It really could be as simple as the 12 volt is old, and needs to be replaced.

Just seems the steps are out of place.
First I'd determine the state of the 12 volt battery in the vehicle. Replace as necessary. Then going forward I might..just might worry about getting a battery maintenance system in place.
But if the 12 volt is healthy, new, and there isn't any peripheral issue, you should be fine with a new 12 volt.

IF there is some peripheral issue draining the battery, then a battery maintainer would only be masking the real problem.

 

"peripheral issues" tend to rear their head when the car is driven infrequently, and short distances. There's always a slightly background draw on the battery. With steady, moderate use, the battery will be ok. Otherwise, I think you do need to consider preemptive strategies, to wit: regular hook up to a charger.

 

It must be remembered, in the context of all the above excellent advice, that the OP's (@Jeff68005) central point was that he does not drive his Prius very often.