Voltage...... 13.1

i would check the battery with a volt meter after being off for 4-5 hours.

 

Since this car has no alternator, you should probably focus on the 12V charging function of the high voltage DC system. It may be an ECU or wiring problem? Hopefully not the inverter itself. Carefully check all related grounds, power and control. The intermittent nature is going to be a problem, of course. Any codes?

I'm traveling, with no access to my wiring diagrams. You may need a good set of diagrams for this. Good luck.

 

Once the 12 volt has been discharged to the point that you need to jumpstart, I don't think it can recover completely without a charging session. Jumpstart will partially revive it, but it's still walking wounded.

 

I've heard excessive idling will run down the 12 volt. And leaving a car running overnight..., ah I better not get started, lol. A 3~4 amp smart charger is a small investment, will save your bacon. Good with this car, the one after, the one after that.

 

Can you afford $53.88 + tax? If so, get this

This is a very versatile charger that will work well on the Prius battery and traditional batteries.

3A/15A charge setting. (Prius will be the 3A setting only)
Wet/Gel/AGM battery selector.
FULLY AUTOMATIC! Make the Amp and battery selection, and walk away.​

If you can spare a few more dollars or don't mind buying a "used" one off Amazon, the CTEKs are really NICE!

 

No speculation. This is totally normal behaviour for the Prius charging system, though surprisingly few people seem to know about it. I've noticed this before, posted several threads about it, and can reproduce it any time at will.

It appears to be a simple two stage charging system, though it does have some quirks. It seems not to happen if the ambient temperature is too cool (which is perhaps why some people never notice it), and certain electrical loads seem to inhibit it as well (particularly the aircon, and even just the fan).

If I go for a drive in reasonably warm weather and don't using any electrical accessories*, then after about 20 to 25 minutes of driving it will do this every time. The charging voltage abruptly drops by about 0.6 to 0.7 below the normal voltage. Mine typically drops from about 14.0 to 13.3, but your readings are not abnormal.

*Note: Not all electrical loads will inhibit it, though I can't remember exactly which do and which don't at the moment. Apart from the aircon and fan that is - they always inhibit it.

 

When the charging system has reduced it's output to the low level "figures on the MFD will vary from car to car as the readout is not accurate" the battery is just being maintained. (float charge) Any load that is sufficient to drop the battery voltage below 12.8 volts causes the dc to dc converter to increase it's output. Motorized item such as the cabin fan, and wipers have very high starting loads, and will trigger this change side lights generally will not immediately trigger it the headlights will.
A battery with decreased capacity will produce this effect more readily as it will reach full voltage more quickly. Your battery if the original is due for change at 7 years old particularly in view of the fact that it has been completely discharged late in it's life.

John (Britprius)

 

Mendel,

Discharging of the 12v when idling is true for most cars, but not our Prii. Our little 12v battery is charged (albeit slowly) by a DC-DC converter in the Prius "Inverter" and works as long as the HV battery can supply power (it is maintained if the transmission is in Park while the Prius is in "Ready").

I have ordered a CTEK 3300 to maintain (and desulfate) my PbA AGM batteries:

• My original Prius battery - still holds a charge after 11 years.
• The battery in my new B&S 8 kWatt emergency power generator
• The two batteries in my electric skateboard - I probably shouldn't ride it at my age .
• My portable B&D jumper battery with air pump
• The Optima yellow-top in my Prius - It still holds a charge after 11 years!

It took a while to convince my spouse that the $65 expenditure was worthwhile.

JeffD

 

I dropped a FAT hint one Christmas, to one of my sons: boy, I could really could use a CTEK 3300. Think he picked up on it?

Anyway, got one on sale, for about that amount.

 

Use of the car and if you left a light on by accident (map light, front/rear overhead dome light, trunk light, etc) and for how long.

Do you frequently listen to the radio while the car is in Accessory mode (foot off brake, power button pressed once) for short &/or long periods of time? YES = bad for 12V
How long is your commute? Longer is better to keep the 12V battery charged.
Same for errands? Longer is better.​

I wouldn't be surprised if some might recharge their battery on a regular basis to keep the battery fully charged, maximizing the battery life span. A discharged battery kills the lifespan. This battery maintenance could be done at what ever interval you want: once a month, every other month, etc. More frequently the better though.

The newer chargers just clamp onto the positive and negative battery terminals, plug into an AC outlet at home/garage, press the settings on the charger, make sure it is charging, then walk away. The charger will take care of the rest. Come back in a few hours or the next morning (assuming you started in the evening/night).

The more convenient chargers (like the CTek) have the battery clamps AND permanent battery terminal connectors that stay attached to the battery; these are fused on the 12V side for safety. This is a really convenient feature, as you don't have to remove a lot of the trunk to get to the battery; just do it once and done. Convenience aside, it is still probably a good idea to check on the spare and 12V battery well, to make sure there is no water, as cracks near the hatch hinges is a known problem. I like this thread b/c the original poster included some nice photos of his water leak issue. Water filling driver side floor pan. | PriusChat

On a brief tangent, check your oil level regularly. Too funny when people come here freaking out, due to the low/no oil pressure warning light (it is not a low oil level light, although that would trigger this warning light). Had they been checking the oil level regularly, they would have known the engine is consuming some oil, and to top off as needed. The more frequently you do it the better: after every gas fill-up, once a week, every other week. Flat level surface, after some period of time (longer is better), so the oil can get back into the oil pan, for a more accurate oil level measurement.

 

I hook up (just with the clamps) at the jump start terminal, under the hood. Its likely imparting some inefficiency to the process, but it's convenient, seems to be working.

I charge infrequently, maybe every 6 months, if that. It's as much for those accidental discharge times as regular maintenance charging. Guess I've had it close to a decade now, used it in various vehicles, not just ours.

Again, a decent digital multimeter is another good item.

 

Last time I saw them in an automotive specialty shop there was some new and improved ones. But anyway, the CTEK MULTI US 3300 (aka CTEK 3300) is what I have. It's been out a while, suspect CTEK is trying (at least in part) to introduce the newer ones to entice consumers to spend again. I've not heard of a 3300 failing. Part of the sales pitch was you could drive a tire over it, it would likely survive. Maybe that's come back to haunt them, lol.

Anyway, there seems to still be a lot of stock of the 3300, it does a charging "program", and if need be can be left on indefinitely.

Downside, it's kinda pricey, but not obscenely so, and it's a one time thing. There are other brands more reasonable though.

 

I have the Schumacher listed in my post #9.

Wrongmart sells it for the same price as Amazon, but it would have to be ordered and shipped to you or ship to your local Wrongmart store.
O'Reily is more expensive than Amazon/Wrongmart, but would likely pricematch. But not in stock. Ship to you or to store.

EDIT: If the wife has a lot of shoes, you know for nearly every single outfit, you are entitled to ONE 12V battery charger.