Battery question

Are you sure nothing was left on, when doors are ajar or convenience lights are left on, the drain is generally on the 12v You are speaking of the HV Bat, right. ? Gliches do appear in the Prius computers from time to time. Possibly even that half charge indication was a glitch and not accurate. Wait til it happens again, then se the dealer.

 

all the best! let us know what they find.

 

Definately a problem there.

 

I see at least 2 bars difference indicated on a HOT battery vs a cool battery. IOW it drops at least 2 bars over night when it cools down.

 

How long of a drive did you have on the day it dropped to half, then 2 bars, and then on the days it was OK?
Did you run on EV mode any?
The reason I asked about how far you drove is because on a cool morning the system will try to use the battery if it can instead of the ICE to allow the ICE to warm up under minimal load. If the speed and accelerator position are such that it needs the ICE it will use it but under low speed and light pressure on the accelerator pedal the battery will be doing most of the work for the first 30 to 60 seconds, depending upon the temperature. This could explain getting down to 2 bars.
I also noticed something a couple of days ago when I was doing a fair amount of driving in EV mode. The ICE came on at 2 bars and the battery slowly worked its way back up to 3 bars. I then went down a couple of steep hills. The first hill didn't seem to affect the number of bars. However at the bottom of the second hill it went from 3 bars to 6 bars. It may have been the case where the number of bars is updated like every 30 seconds so the sample/update rate was too slow to catch the first hill and the amount of regen it provided.

Good luck. Hopefully there won't be any issue for you.

 

It sounds like you have some sort of drain, maybe even a short circuit draining the HV Batery. HV = High Voltage.

 

Loose connections can alsodo this

 

The battery gauge is a guess at best. There's no foolproof way to tell the amount of energy stored in a battery without draining it. Basically what the Prius does is while you drive it, it counts how much energy goes in, and how much comes out, and uses those numbers to update the gauge. When you turn it on, it's in a better state (usually) to get an idea of how much is stored by the voltage alone (which, when driving, can fluctuate due to recent charging or discharging or heating), so it can recalibrate the gauge to a certain extent.

So, assuming that your car is in fact being turned off (the battery is physically disconnected from all possible loads when the Ready light is off), then you're not losing any energy from your battery - the gauge is just showing normal inaccuracies.

 

not necessarily the car keep estimating the charge in the battery from measuring currents in/out in hotter tempreature higher load (A/C) this guesstimate can be out of whack quite a bit by the time you stop.

I have seen both higher or (mostly) lower indicated bars next startup. At startup the computer again "estimates" the SOC but at this time it can do a lot better job, no overheating cells most likely not having static charge on them so from temp and voltage it can pretty well estimate SOC .. then the game start again and computer calculates SOC not measuring it.

 

From your initial post, I would say there is a problem. No matter what the dealer says, keep an eye on it.