12v battery jumping and replacement options

Have you checked the resting voltage of the 12v battery? I am sure if you find your 12v battery dead within 3 years, then you can demand it to be replaced under general warranty, but they may ask you how often the car was driven or the battery was charged. Hard to believe that by just sitting on a dealer's lot for 5 months the battery dies prematurely, but I have read enough threads here on both Gen4 and PRIME 12v battery early demises, so I am being proactive and monitoring my 2020 PRIME's 12v battery SoC very closely using Bluetooth Battery Monitor and not letting it go under 12.4v. Replacement aftermarket H4 or L1 or 140R BCI group size (8.1" x 6.9" x 7.5") 12v batteries are now readily available and cost about $100~$160. But OEM battery is not that expensive ~$180 last I checked. When it's time for me to buy a new 12v battery, if that day ever comes, I plan to negotiate with a local Toyota dealer to install a battery for $99 as advertised on their web site service coupon.

As for the jump starter, I bought DBPOWER 2000A 20800mAh Portable Car Jump Starter last year, but have not used it yet. For Prius, you do not need a huge cranking power, so even a very small lithium jump pack will do the job. I think you may also want a good smart battery charger/maintainer if you are worried about the 12v battery health status. Many people suggest CTEK chargers, but I ended up buying Bluetooth enabled Victron Blue Smart IP65 charger. Blue Smart IP65 Charger (120V and 230V) - Victron Energy

 

Charging the traction battery does not charge the 12v battery substantially. It only maintains at voltage around 12.5v, and this happens only during the time the traction battery is actively being charged.

No, it is not AGM. It is a regular flooded lead-acid battery. The OEM battery is not even sealed. It has vent caps on it. That's why replacement battery should not cost as much as for the older Prius with AGM. I have read pros and cons of AGM. Although some people believe it is better, AFAIK for now finding an AGM battery in the size required to fit Gen4 Prius or Prime is difficult.

Your battery voltage reading looks very normal of a healthy 12v battery. You may want to follow this thread to see what others are seeing. There are some 2-3 years old 12v batteries in the Prime which seems to have lost capacity especially now with COVID-19 restriction and less driving.
12v Battery Is Discharging, Re-Charge Now ! | PriusChat

 

There is a lot of discussion on 12V replacement in the Gen 4 Prius Hybrid section (not Prime). They have the same 12V battery...

 

Just the opposite.

 

a lot of people agree with you. see @Rob43 's thread on 12v draining per day

 

To do that would have required connecting the traction battery to the inverter the whole time it's plugged in. I suspect there are safety as well as energy efficiency reasons for not doing that. Plus, it would be a pretty sad day to wake up one day and find that your unnecessarily plugged in Prime got fried by a lightning strike. It could still happen, but it's less likely if you're not connected to the wall all the time. In fact, I went outside in the rain a few minutes ago to unplug mine because there was lightning in the area.

 

Not out of the box, but I think it can be custom programmed using an app to be just battery-tending voltage. But my understanding is that if you use a smart charger like CTEK, going through the normal charge cycle does not harm the battery. On my Victron charger, there is mode selection to include "reconditioning". The manual does suggest not to overuse the "reconditioning" mode. I am not sure if CTEK charger has the selection of the mode, but if it harms the battery to be used all the time, I would think it has a way to not use it. If you simply want a battery maintainer, there are other less expensive ones, but I have read cheap ones like $5 HF battery tender is set to just the very low constant voltage and it may overcharge the battery over time. So, again it may be wise to invest in a charger that does control the charge level according to the battery level.

I hope others more knowledgeable than me will chime in on this topic.

 

I have been doing with the hood open. It is not too much work, but as a part of mod project on the front grille cover I am working on right now, I am planing to install exactly what you are describing. A on board battery charger will be housed under hood and connected to the 12v battery post permanently, then charger cord will be attached to a cable extension with a male plug in hidden behind the license plate. This will be easier to connect and recharge the battery with just a plug-in an extension cord from any power outlet. I will report more when I have the project finished. At this point, I only have the parts ready but have not done any of modification yet.

 

I have never heard of OBD connection to charge the 12V battery. But, since there is OBD connector to supply 12v power to the car during on-board 12v battery removal (to save all the memory and prevent re-initializing the car), I guess, you can charge the on-board 12v battery via OBDII. But, I have no idea how that works or how safe it is. @Rob43 has a DIY solar panel connected to his 12V battery but I don't think it goes through the OBDII port.

 

I don't know about the safety. Connecting a charger to the 12v battery under the hood is just as safe IMHO. One problem of using OBDII connection to charge the 12v battery is that you will have to connect your charger/tender and to the wall 120v power source, so the cord has to be going out of the car from cracked window. With under hood connection, even without special connection cord or on-board charger, you can keep the charger under the hood and feed the cord through the grille and close the hood securely. However, since I don't have problem with security, so I just keep the hood popped open when I charge my car.