How long should 12V battery last in accessory mode?

Yeah, so if you need to run accessories and stuff off the Prius, do it in READY while parked. Even though it will drain the high traction battery, the motor will kick on and recharge it.

Also, if that 12v you have looks like the original that came with the car, which wouldn't be a surprise because its only designed to power up the ECU and therefore would last a very long time, I would still suggest replacing it. Funky stuff starts to happen when the 12v battery's charge drops too low.

 

It is true that several parts of the 'video game' that is the Prius are a sloppy emulation of 'real' cars.
There is no alternator, so your headlights do not get brighter when you rev the engine up. One section of the inverter converts 201 volts DC to 12 volts DC (actually about 14.4, so it can charge the 12 volt battery) This is unlike other cars in general where the engine is much more involved in making 12 volt electricity. (alternator, voltage regulator, etc.) Because the 12 battery never runs a starter motor, it can be smaller than usual for a car but this also means the Acc mode lasts a very short time and leaving the dome light on can drain the battery before dawn. (Another issue, how good are you at recognizing a dead or dying battery when it never makes the slow starting noise?)

I like this guy:

(15:15 to 18:00 explains the 12 volt charging)

 

Lucifer, the battery isn't all that bad, but I have learned to turn off the dome lights in my '04 Prius. Saved a many a dead battery.

 

Check the Owners Manual for second gen requirements, but if it's like third gen, you don't want to exceed 4 amp. 3~4 amp is good range. It should be an up-to-date smart charger, the kind that runs through charging cycles, monitors the battery's condition, wrapping up with a very low maintenance charge level, so that it can be left on indefinitely if needed.

I'd recommend the CTEK 3300, but looking around they seem to be getting rare. There is a CTEK replacement for that one, and several manufacturers in the same field.

Maybe something like this:

NOCO Genius G3500 Smart Battery Charger | Canadian Tire

 

My 2004 Gen 2 12 volt battery made it almost 10 years. It was still starting the system but my mileage dropped like a stone.

I let Toyota replace it, since it made it about ten years. Now that was two years ago. My car may get driven everyday or it may sit for three or four days. My mileage is erratic, my belief is the car is charging up the small battery and recharging the HV battery, too. If I drive it daily, my mileage over the entire tank is higher, too.

LG G3 T-MOBILE phone ☎

 

I just got a rude awakening: in Canada at least, the stock 3rd gen battery, YUASA S46B24R-GS, is going for $273 (CAN) at the dealership parts departments. I contacted a couple, one's usually higher than the other, but they're both saying $273. A year back they were around $205~$215.

Last battery I bought was a conventional one for our daughter's Pilot, maybe 6 months back, it was around $150.

 

Mendel,

Autonation is selling the 12 volt here for $206.40 BATTERY for 2013 Toyota Prius|28800-21171

Of course the part # is different from the one you quoted, but that is what they are listing for the Gen III Prius.

I also note that YUASA released a new ECOR line http://www.gs-yuasa.com/gyin/en/topics/pdf/20140618e.pdf that seems to fit the Gen III also.

Ron (dorunron)

 

I'll check that out, thanks. The $ differences start to dwindle tho, when I factor in our 80 cent Canadian dollar plus duty.

I read global warming, and milder winters, are causing people to stretch battery life, so with battery returns down the cost of new batteries had to climb. Not sure if that makes sense, but it's the story, lol.

 

Shipping was $135, from AutoNation. Then there's the dollar conversion and duty.

Toodle down to local dealership with fistfuls of $'s still cheaper.