fix or replace?

It would be best if you could the car drive more often than twice a week. If you cannot fit three or more drives in this vehicle of 20 minutes or more for each drive into your normal daily schedule, then you should consider obtaining and using an automatic multi-stage 12 V battery charger and use it when the car is not in use for 3 days or more to maintain your 12 v battery in a healthy condition.

 

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it is possible that something is draining the 12v while the car is off. but hopefully it is just the lack of driving.
determining which it is would take some testing. if you can't find a private hybrid mech, you might be better off selling and buying a non hybrid. it sounds like your dealer is clueless.

 

If this means you got a “new” reconditioned hybrid battery somewhere you really bought a used battery spit shined to look good for a short time.

There is a constant 12v draw on a car even when off but it’s is so small that a good 12v battery should not need a battery maintainer if driven once a week. However there can be abnormal drains like lights, aftermarket gps or radio or even an obd2 reader left plugged into its port. Or something more serious, eg an excessive “parasitic drain”. A decent mechanic or a good diy’er can measure that drain with a $3.99 Harbor Freight meter. If an excessive draw is there the skill comes in to pinpoint the location and fix it.

Unfortunately a standard Corolla or Camry 10 or 15 years old would be far more reliable and much less costly to fix than one of the most complex cars ever made, eg a Prius.

If most of the current problems turn out to be battery related (maybe both batteries) then fix the 12v drain and or get a new Toyota OEM hybrid battery, often available for $2k-$2.5k.

 

Noco chargers are good, but I'd go for one with a 4 A output rather than that 1 A. The advantage of the 4 A charger is it will charge faster (4 x) than the 1 A.

 

i only use mine as a maintainer. it should keep the battery full for people who don't drive much unless there is a serious drain when off.

 

True enough but a higher amperage unit will charge a low battery faster and will trickle charge when full so it is the best of both worlds.

 

Beware...

Harbor Freight sells a nice little charger which is advertised as a 4A charger:

4Amp Fully Automatic Microprocessor-Controlled Battery Charger/Maintainer

Well, it is apparently 4A at 6V but 2A at 12V, or at least that's how it looks to me, since I have never seen it put out more than 2A at 12V. (It may vary from unit to unit, I'm not convinced that the part number at that store always corresponds to the same exact part.) The only other problem I have had with this unit is that it gets confused by surface charge and will not always charge the battery. Other chargers might have this issue too. I suggest turning on the headlights for a minute or so, then turning them off, then turning on the charger. When I have done that it always charges.

 

I can't predict the condition of your car but assuming it's typical for that mileage i'd definitely put a new hybrid pack in it and happily keep driving it another 200k miles.

My own belief system is that a cars value is not wholly dependent upon a book statement of value....but mostly based on its predicted life remaining. Since I believe it has another 200k of usable life, and I don't care about modern tech in a car, it's worth a lot more than book.....

If you value a car that looks good then it's not worth much. I personally don't mind some scratches and peeling paint. Occasionally I notice new scuffs from other cars that apparently hit mine in a parking lot. It rolls off of me because mine is already scratched. My Toyotas are commuter cars. Appearance isn't important. Money saved is...

 

The 12v battery in my 2008 Tspirit (UK) was last replaced in 2014. It is still running flawlessly. I’m slightly mystified as to why it’s lasted so long. The last one was the OEM 12v battery which only lasted 2008 to 2014.

I did have an auxiliary battery installed under my seat in January 2019, to power my dash cam (dual camera) 24/7 specifically in parking mode (after the theft of my catalytic converter in November 2018, and a hit and run from the rear prior to that).
This auxiliary battery lasts 36 hours approximately. It’s charged by the HSD during my commute and will fully recharge in 45 minutes.

I’ve often wondered whether it’s somehow also charging the 12v during parking mode until it runs out on the weekends if I don’t drive for two days - or otherwise supplying power to other passive systems normally run by the 12v when parked - though I doubt it.
It was installed exclusively for the dash cam however and shouldn’t be running anything else.

Maybe I just got lucky!

The only other thing is my daily commute is a 34 mile (UK) round trip 5 days a week - virtually every week, not counting the occasional weekend trip.

I still have the OEM Traction Battery too, which was checked by Toyota last December 2023 and found to be in perfect condition.


iPad ? Pro

 

High temperatures tend to deal the death stroke to these batteries, but the negative consequences of death don't occur until you try to use them in cold temperatures.

For many versions of the Prius, the battery gets a major life extension by not being under the hood bonnet where it would be subject to a nonstop blast of 60°C air.

The point is, Autumn is a great time of year to replace an older battery that you're wondering about. You get the most time-in-service while dodging the most likely time of failure.

 

Is it wired in parallel with the regular 12V or is it separated from it with a diode or relay (so charges when the car is running and "12V" is more like 14V, but afterward current only goes to the camera)? If it is in parallel then it would take some of the load off of the regular 12V even beyond what your camera pulls, and that in turn would help keep the state of charge (SOC) high. Some cameras pull a substantial amount of current, and the Prius 12V is not very big, so the extra battery was a good idea.

That said, the bigger factor is probably that your commute should be long enough to keep the (regular) 12V fully charged most of the time.

The AGM batteries last longest if they only rarely drop below a high SOC, and even more so, never get to a low SOC.