Battery maintainer install directly to 12V battery

Gen 3 is in the hatch like that, and positive is on the left. There should be + and - embossed on the plastic, it's pretty much mandatory. Hopefully not buried under all that rigamarole. Also, positive post is usually bigger diameter.

Consider wiring it under the hood too, at the fuse box (positive) 12 volt cable's connection, and neg lead of the charger to a ground (car body).

 

^ This is an excerpt from page 592 of your Owner's Manual. In the warning below pic, it would have been helpful, for toyota to identify the pos and neg terminals in the picture. Anyway, the plastic cover on the right side connection (I've highlighted in yellow, "might" indicate it's positive. Look for corraboration: again, positive post is typically bigger diameter, and you may be able to spot pos and neg logos on case.

Also, there will invariably be a cable from the neg post to the adjacent body.

If you've got a test light: clip it's ground cable to bare metal on the body, and touch one post, then the other. The positive post will light it.

Test lights are around ten bucks:


You can sub a multimeter set to ohms, or continuity, another way to do the above test. Clip neg lead of meter to car body, and touch positive lead to one terminal, then the other. Whichever drops ohms to near-zero is neg.

 

If you find the symbols (they should be there) maybe mark them with something contrasty. Again, consider the test light or multimeter tests.

 

Yes, you should definitely hook up the Noco Genius if you don’t drive the car for longer than a week. The battery loses about 20% SOC each week, and the normal SOC stays around 80%. This means, it completely drains in four weeks, and even if it doesn’t, sulfation intensifies with the decreasing SOC.

You can directly connect it to the negative terminal of the battery. The reason for the caution is to prevent sparks igniting potential hydrogen gas near the battery. Simply fan the battery to disperse any potential hydrogen gas. Moreover, the Noco Genius does not turn on until you press the on/off button; so, as long as you don't turn turn it on before you connect it to the battery of turn it off before it fully completes the charging profile (the green LED becomes solid and stops slow-blinking), there cannot be any sparks to begin with. You can also disconnect the 120 V AC plug first and wait for ten seconds, which would energize down the device, if the charging profile hasn’t been fully completed. Or perhaps long-pressing the on/off button will turn it off (short-pressing will toggle between flooded-cell/AGM/lithium-ion modes).

In addition, the Gen 5 battery is ventilated outside with a hose, and there shouldn’t be hydrogen gas near the battery. I think there are also battery-connection posts under the hood if you prefer connecting the Noco Genius there.

One last thing: I would connect the Noco Genius directly on the negative battery post rather than the negative-cable post to bypass the shunt resistor that measures the battery current. It is not a big deal though.

 

While you're at it, I would strongly recommend attaching a little voltmeter across the battery, with leads long enough so that you can run it into the back seat and see the meter without opening a door or otherwise waking up the car. They are dirt cheap from China, inexpensive (C$10) from local sources (e.g., MINI VOLTAGE DISPLAY, 2.5V-30VDC, 2 WIRE CONNECTION).

 

No, I have something much better installed than that! You should definitely get this one, too. It records the accurate battery voltage vs. time on your phone.

BM2 Bluetooth battery monitor on Amazon

 

@th27000 did you remove anything in your pic? See location of red plastic cover, indicative of positive terminal:

12v roundup | PriusChat

really though, trust but verify, with verification of of + and - symbols atop case, and/or test light or multimeter verification.

also again: consider wiring your charger under the hood, at the fuse box. That’s what I’ve done with my ctek 4.3 charger’s quick-connect cable. It’s convenient, you can either sneak the cable out under the partially ajar hood (if in a secure garage), or out the front grill.

if this is daunting, consider getting a mechanics advice/help, a misstep CAN fry expensive wiring and components.

 

Here's a video, albeit 3rd gen specific, regarding accessing the optimum 12 volt positive point in the under-hood fuse box:

It's video #23 here, for future reference:

Nutz About Bolts Prius Maintenance Videos | PriusChat

5th Gen "may" be similar enough that it helps.

 

If you can return the Noco 2D, see if you can get the Noco 2A, which has the alligator clips and eyelet connectors. The eyelet connectors are screwed to the alligator clips and can be removed.

 

Looking on Amazon just now, the 2D is described as on-board, and has the eyelets. I clicked on the left side link in this:



It's a little bewildering to say the least.

 

You can use a jumper cable.

The Noco Genius 1 A would be sufficient and has alligator clamps.

 

I have my maintainer charging out in heavy rain right now. Actually on gen 4 there is like a tray to lay a small charger in. I snake the thin power cord out through the headlight gap and lock the hood. The extension cord and charger plug cord go on top of the front tire. It came with the eyelets but I use the clamps and clip it on directly to the battery, before the battery sensor on the neg side.

 

I did something similar for my FJ during the COVID pandemic when we worked from home. I used a Motopower battery maintainer with an extension cable with caps to close the connection when not in use/charging. I connected the cable to my battery terminals and allowed the end of the cable with the capped plug to stick out slighty between the hood and headlight. I could then connect the Motopower to it and run the cable from inside my garage under the garage door and to the FJ.

 

I attached my NOCO genius 2D directly to a 12V lug in the forward fuse box under the hood. I find this location more convenient than opening the rear hatch.

 

My setup battery tender hooked up to battery + - plug on outside capped so no salt enters as soon as I get home car is plugged into tender
My backup just incase

 

Does the trunk seal well around the cord and seem to be okay closing around it so often (that is, when you open the trunk does it look like you're wearing a permanent groove into the seal itself)?

 

Fatcato No issues whatsoever