Hot days discharge battery?

Recently it's been 100+ degrees here.
On hot days when I get in the car after it being parked for an hour or two and the battery is down to 2 bars.
Is this due to some kind of cooling fan on the battery that allows it to drain itself to prevent heat damage?
Or is something wrong?

To know where we're starting from, what battery reading was the car at when you parked it? A little loss might be expected just from startup motors and pumps when you open the door.

Starting one or two bars from the top.

I've observed this too, and I think that it's an artifact of measurement. The battery is unlikely to self-discharge by such a great amount in less than weeks or even months. Most likely, the system that determines the state of charge also takes into consideration the battery temperature, and gives a "false" reading until temperatures normalize.

If the battery really went from almost full to half-full in a few hours, it would be truly empty by the end of the day, and you'd have heard the howls long before now.

Richard

I looked at similar posts for the II, but nobody reported actually determining a cause or defect from what the owner saw as rapid discharge. Most suggested that unless it was accompanied by low mileage because of near constant use of ICE or a failure to ever return to higher charge levels, it is probably just as Richard says and not anything to be concerned about. The remote AC no doubt would cause a drain but it has a cutoff for low battery power.

You are turning the car off while parked for an hour, right?

Instead of showing discharge, is the indicator showing the effectiveness of the batteries, adjusting for temperature?

Yes I am sure the car is off.
This has happened several times, and always when hot.
I just assumed it was some kind of cooling fan that was drawing power from the battery. But I figured maybe someone else would know for sure.

I'd like to follow up on this. I've only had my Prius for a week, but I notice that every morning the battery indicator will show that about half of the charge has dissipated during the night. I haven't had a chance to do much driving this week, only maybe 15 miles per day, and like I said, it's a brand new car with, now, around 115 miles on the OD. When I park if for the night, it will be around 2 bars from the top. When I get in it in the morning, it will be around 2 bars from the bottom. Normal? I haven't noticed any issues while driving it. Does it just need to be broken in/driven more?

I have never seen this. Not even over longer periods. Very often I have it parked over the weekend and Monday morning the battery SOC is exactly where I parked it Friday afternoon. Granted, we don't have much temps over 30 C, but I did on my holidays in France, and never noticed this. Definitely doesn't seem normal to me.

I'm experiencing the same thing. When I don't drive for a few days, I notice the battery has discharged substantially. It will be down to 2 bars (after being near full when I park).

I'm sure you've considered this, but just in case you haven't - where are you're Smart Keys during this period - how near to the car are they?

Edit:
Sorry - that's rubbish. This from the manual:

[FONT=Arial,Arial][FONT=Arial,Arial]Battery-saving function [/FONT][/FONT][FONT=Arial,Arial][FONT=Arial,Arial]In the following circumstances, the entry function is disabled in order to pre-vent the vehicle battery from discharging and electronic key battery from depleting. [/FONT][/FONT]l [FONT=Arial,Arial][FONT=Arial,Arial]When the entry function has not been used for 5 days or more [/FONT][/FONT]l [FONT=Arial,Arial][FONT=Arial,Arial]When the electronic key has been left within approximately 6 ft. (2 m) of the vehicle for 10 minutes or more.[/FONT][/FONT]

This sounds like it is reproducible. I would recommend:

1. record trip meter data when you get home, don't clear it.
2. record trip meter data when you go to start and then clear it.

If the trip meter data shows the MPG went down, the car somehow was not turned off or stayed off. It continued to stay "Ready" so it simply continued to run. The decrease in MPG while parked is the clue.

GOOD LUCK!
Bob Wilson

Interesting. I'll try that. Thank you.

BTW, I got in the car yesterday after not driving for a few days. No discharge. So...go figure.

A change in MPG would suggest that ICE had been running. Wouldn't a drop in average MPH be a good indicator that the car stayed on?

It's been over 105 for about a week and I haven't seen this happen. It was 112 on Saturday and I didn't see this behavior. I wonder if something is draining your battery.

I see this occasionally on my '04. It seems to be random.

Always lock the car, to help avoid situations that can drain the battery.

I have had my Prius for only a few days, but I am noticing this too. I live in Arizona, so it is very hot, and I leave my car out in the heat for 9-10 hours while I work. When I park it in the morning, it is one or two bars from the top, and when I get in after work, it's down to only two. This has happened consistently 3-4 days.

This seems to have cleared up for me. In the first week and a half I wasn't driving much, and also had taken the car in to have leather installed. But as I've been driving more the last week, it seems like my battery has had a chance to "really" build up a charge, and so I haven't seen any discharge lately.

I noticed this the first week or so as well, but it didn't seem temp related. The battery appeared to discharge overnight or over the day at work. After the first week, the battery didn't show as discharged when starting, but after only a few seconds of driving after startup, the SOC would drop really quick. Now, after almost a month, the battery seems stable without total or quick discharges.