Install 12v battery maintainer under hood?

The battery tender I have for my motorcycle has a little plug that's easy to connect/disconnect. I'm betting the bigger ones for car batteries have something similar. I'm sure you can find a way to route through the grill like a block heater cord so you don't need to open and close the hood every day.

 

I've been toying with the idea of an on-board charger. I'm surprised Toyota doesn't offer it as an accessory*; with a location and install procedure worked out. It's really the way to go, and typically you'd have (similar to block heater) a male 120 volt AC plug at the front grill. You can get fancy, put a special port in the bumper, but a simple plug-and-cord, zip tied to the front grill would work fine. It's more secure than an external charger, say if you're parking in an exposed carport.

I'm currently using a CTEK 4.3, external smart charger, but I've got a secure garage, so no big deal. But if it fritzed, I might look into on-board style charger. I believe it was @MSantos, recommended a Noco on-board charger a while back. Noco has this new one, which looks interesting (Amazon Canada screen-grab, with price in CDN dollars):



* Toyota does offer an on-board charger for the 4-Runner; insanely steep price though, around $500 CDN IIRC.

 

There really is no good reason to do that.......unless maybe you live where it is REALLY cold and you can plug it in every where you go.

The 12 V leads can be extended out through the grill, for instance, so you can plug it in at the low voltage point.
Those connectors with a "dust cap" can be had at any auto parts store.

 

The battery maintainer (smart trickle charger like a Battery Tender brand) need only be used when the Prime is left parked for several weeks or more. Don't keep the main charge cable plugged into the car in this case. The gasoline engine does not charge the 12v battery. It is charged from the traction battery. Back to the question--no problem keeping the 12v battery charged in cold weather, but probably not needed. The 12v battery powers the electronics to get the car into Ready mode. You don't need much amperage to maintain the charge. One amp is probably sufficient.

A ring terminal harness with an SAE plug is available at most parts stores for use with a battery maintainer which has the SAE connector in its charge cord--or add one. The better harnesses have a fuse included, as well as a weather cap for the plug.

 

And that is another reason to NOT bring the AC cord out through the grill.
It will NOT be fused and if pinched it could cause a significant safety hazard.

 

What thing? The 12V charger or the traction battery charger?

If it's the 12V and the battery was very low, it might not be done charging.

If you mean the traction battery charger, then that just puts a trickle charge into the 12V and that's only while it's actively charging the traction battery. If it's not charging the traction battery, it's actually increasing the drain on the 12V.

 

The 12v battery is charged only when the car is in READY mode. Charging the traction battery does not charge the 12v battery. It maintains the 12v battery only while the traction battery is actively being charged. On the other hand, if you keep the traction battery charging cord (either L1 or L2) plugged in after the charge has completed, then it will drain the 12v battery quicker. This is due to the system checking the charge cord connection and traction battery charge level. This uses the 12v battery. The owner's manual recommends not to keep the charge cord plugged in after the charge is completed if you do not intend to use the car for a long period.

 

How long do you drive every day? Very short trips are not long enough to replenish the 12v battery level, but I have found a trip duration of longer than 1 hour at least once a week was adequate to maintain a newish 12v battery topped up.

Have you checked the current state of health of your 12v battery? If you have a load tester, you can check it yourself, but if not, most Auto supply stores will check it for free. If you have let the 12v drain even once by say leaving the radio on ACC mode too long, then your chance of having a problem keeping the 12c battery charged increases.

 

This is very unusual. I don't know if very short drives will result in the 12v battery discharging. For your 2021, you might have a warranty claim for whatever parts are failing to keep the battery charged, or maybe a defective battery. Our 2017 battery remains good. Your new battery should not have this problem. Open the hood. Grasp each battery cable near the battery and wiggle it. Is either one loose on the battery post?

A voltmeter that slips into the accessory socket (we used to call it the cigarette lighter socket) will tell you a lot. They're cheap, $12 on Amazon.

 

There's no voltage going to that socket when the car's off, and when it's on you're seeing an eronious value, due to electrons supplied by the hybrid battery. Best measure voltage somewhere where there is voltage, when the car's off. Simplest is at the battery posts, and then further downstream, if loose connections are suspected.

 

Not a problem. For years, I've been plugging in my L2 EVSE as soon as I get home from work. The schedulers finishes the charging just before I leave in the morning. Still running the original 2017 12V battery with no problems at all.

This. ^^ Repeated short trips will not give the car time to replace the parasitic losses while it's "off."

Although, I never drive more than an hour at a time except on vacation trips. Although I do lots of 30-40 minute each way trips.

 

I am heading overseas for 5 months and my prius prime 2017 will be parked. Last time I went out for 4 months, my battery was dead and had to replace it. I bought a solar charger with the cable shown below. I went to Midas to install this under the hood for the 12V battery. I am hearing conflicting info that the traction battery needs to be maintained as well.

Do you guys know if my Solar charger (which has a circuit to not overcharge the battery) and connecting to the 12V battery under the hood will do the trick this time or I will need a physical person to manually start the car once a month for 15 minutes to recharge. Any help will be much appreciated.

 

I'm using the Noco Genius 1 on my 2018 Prime. It's been parked for almost 6 months so I'll report back on whether it starts or not!

Parked it at about 35-40% traction battery charge I believe (just in case someone wants to know).

 

There are not many reports about how the Prime behaves IRL after having sat for more than a month or two.
I'm pretty sure that if there were reports for half to a year of sitting, there would still be conflicting reports due to at least varying conditions that are beyond our eyeballs so far.
The owner manual has a brief section on how to store the Prime. See post #10 above.

 

Do you know when you will know if your Noco Genius 1 solution worked, because the only difference is that you are using an eletrical source, while I am using a Solar panel and both are trickle charge to maintain the 12V. I am heading out by the end of this week.

Last time I put my EV battery at 80% charge and really it didn't drain at all. But back then the car was only 2 years old. Now the car is about 5 years old. 12V battery was replaced 2 years back, when it drained completely and didn't charge.

 

Sorry - it will probably be another month before I get back to test it out.