12 volt battery recharging in 2012 Prius

welcome! it is possible that you don't drive enough, or the trips are too short. i drive about 9,000 miles a year with no issues. there could be a drain on the battery that they are missing, it's hard to know.
one important thing is to keep your fobs at least 15 feet away from the car, or they will 'talk to each other' constantly, and drain the 12 volt.
you may want to consider replacing with an aftermarket 'optima' battery which is a little more robust than the toyota.
it takes a lot of driving to charge the 12v, i don't think idling will help much.
another alternative is to hook up a trickle charger if you have a garage.
all the best!

 

The 12 volt battery is charged by the Inverter/Converter whenever the car is in READY, no need for the engine to run, nor does it charge any faster if the engine runs faster.

Mind you, the Inverter is powered by the HV Battery, and if the State of Charge of the HV Battery gets low, it will be charged by the engine; but the 12 volt battery itself is not charged by the engine.

At 6:30 there is a brief mention of 12 volt charging, more depth is at 15:15 to 18:05

 

Since the voltage wasn't checked when the "new" battery was installed we don't know how good it was. Since the battery only lasted 8 months either it was defective or there was some drain on the battery that you didn't notice. I'd expect a new battery under warranty and check the voltage before it is installed. Dealers aren't immune to selling defective batteries.

 

That's mostly nonsense. An hour of "READY" time per week might suffice, if there are no unnecessary drains.

I agree with bisco's suggestion to consider employing a float ("maintainer") charger if practical.

 

do you trust them on this one? i wouldn't.

 

If you've got a digital multi meter you can check the amperage when the car is off. You need to disconnect the the cable between the body and the negative battery post, then put the meter into the circuit in series. Specifically, connect wires from the negative battery post to the meter, and from the meter to the body. Use long wires, run them out over the hatch opening, lay something (say a glove) over the hatch latch mechanism to defeat it, and gently lower the hatch onto the wires and glove.

Set the meter to amps first (for safety, in case there a large flow), then if it doesn't register anything, switch to miliamperes. Do NOT open any doors during this test, do anything to wake the car. Normal would be values around 15~20, with occasional ticks to around 40.

 

Driving that short distances definitely taxing the 12V battery simply the "cold start" takes out more "juice" then you can put back driving 4 miles ... it takes 30-45 minutes to driving if you had a reasonable charged battery before starting. So your 12 V battery is getting lower and lower SOC. Which is really do damage to any 12V car battery (there are some deep discharge type but the prius' is not one of those).

Leaving the car in Ready mode will help. The HV battery charges the 12V battery and when it is in Parked the computer raises the charging voltage somewhere around 14.6 V till the the battery is charged. BUT only do this in a safe environment NOT in the garage since the ICE will come on time to time.

Better yet to have a battery charger which can charge it (also floating charger) . I believe the recommended current is about 4A or less. You can use the port under the hood to hook up .. this is kind of labour intensive solution.

" An hour of "READY" time per week might suffice,"

Not really!! If you start up the car a few times a day and drive it just a few miles each !!!

When the prius starts it takes quite a bit of charge out from a relatively small battery (main brake cylinder charge and all the other initialization) someone here made the proper calculations so we DO KNOW that it takes about 30 minutes to replenish that charge (per cold start). The charging circuit is really charging the 12V battery very slowly.

I actually monitored this myself with scangauge. If no other load (lights wents ... etc.) and you put the car in park it will show 14V+ volt while 12V battery needs charging... then it shows 13.6 consistently. Depending also on temperature wheterh I drove previous days, I found that 30-45 minutes driving when those change. My commute is double that and has many lights so I was able to field test this.

 

In addition to what bisco was saying there is also the proximity interior lighting feature (I have mine turned off). I don't know the actual power draw but it might be a gremlin if you walk near your car often with the fob. I had a similar dead battery situation in an older Lexus LS. I purchased both a Sears Diehard 12v battery charger/maintainer and a solar type off ebay to keep handy if needed.

 

??? If defeating the latch mechanism with the glove means preventing the latch mechanism from reaching its fully latched state, the effect will be the same as leaving a door open, resulting in a steady drain of about 0.7 amperes (700mA), PLUS the current to power any interior lights that are on with doors open. To avoid that extra current you have to force the latch fully closed despite the long wires running out over the seal, or (much better and easier solution, in my opinion), forget the long wires and fool the latch mechanism by pushing it to its fully latched state with the hatch still open.

 

Hmm, maybe I did that. Got to admit I hesitated a bit typing that. And yeah, I know if the hatch is open, the front footwell lights go on.

I'm gonna go with I did close the hatch completely, and there was enough give in the hatch gasket that it was no problem, the wires didn't even flex much.

I'm still not 100% sure, because I'm pretty sure I didn't have to crawl through to open the hatch. One of life's mysteries, lol.

I do recall the milli amps was down around 16~18.

I guess it's moot, sounds like the OP's issue is likely low usage. We're in the same boat, just monitor, and occasionally hook up a charger.

 

not from the 12V battery in a hybrid. HV battery does the "cold start" part.

 

wrong choice of word I guess ... "cold boot" up the system maybe a better way to say it. This is all happening of course before the ICE starts which indeed the HV battery does. But the point is that it takes more than a few miles (actually it is time really) driving to put that energy back to the 12V battery and if you do this a few times a week and never drive the car long enough you end up an undercharged battery most of the time which is very bad for a lead-acid battery.

 

So has anyone actually measured how many ampere-hours are actually extracted from the 12-volt battery by a "cold boot"? Whatever it is, it adds to the losses from the brake pump cranking up after every time the driver's door is opened, the 0.7 amperes while any door is open, the lights, the constant 16-18 milliampere drain Mendel mentions, the whir-thump-clunk routine in the first couple of minutes after every shutdown, the evaporative test a few hours later, etc., etc.

This car carries out a war of attrition against its own battery, even without making it crank the engine!

 

We tend to use our car every second or third day, and yeah, it seems like the battery capacity is slowly drained as it sits. Been thinking idly about some sort of cut-off switch. Downside though: loss of trip meters, radio presets and so on.

Rolls Royce would be something that employs flash memory for the above presets, and automatically disconnects the battery at shutdown.

 

Anybody have the current model number for the Optima yellow top replacement in 2012 prius plugin
Optima site says no match

 

should be the same as lift back.

 

amazon.com/Optima-Batteries-8171-767-DS46B24R-YellowTop/dp/B006VFEJJQ

 

Actually, starting up the car takes very little power out of the 12V battery. It's a high current pulse of around 50 Amp but only for half a second. Not much power. What takes power out of the 12V battery is sitting in the car after turning it off without opening the door (the headlamps may not turn off). Or sitting in the car listening to the radio/sound system in other than "ready". Or leaving a door open, or having the hatch not properly latched when the car is off. Just the interior lamps draw over an Amp. The headlamps draw in the range of 5-10 Amp depending on type (for the pair, low beam).
Always use "ready", never "acc" or "ign on" (depress the brake pedal when pushing the "on" button).
Oh, and don't use "N" unless you absolutely have to. The traction battery won't charge in "N".

A lead-acid battery, which is what the 12V is, is not efficient in charging. It takes quite a bit of time to put charge back into it. Just putting the car in "ready" and having the system voltage go to 14+ volts isn't good enough to maintain full charge unless it's kept there for at least an hour per day.

Letting the car sit for a few days will also deplete the 12V battery charge level.

I use a "Battery Tender" connected to the "boost point" under the hood in winter to keep the 12V fully charged when I'm not using the car for weeks. There are other makes, some better, some worse.

Even when you take care of the 12V battery, in a Prius they seem to only last 3-5 years. In the FJ Cruiser, I'm still using the original (2007) Panasonic 12V lead-acid battery. I have to "top up" with distilled water every few years, but it's still working just fine.