Why doesn't the battery ever charge fully?

When it is filled up, there is no room left for regenerative braking. If this happens at the top of a hill, then all the potential regeneration of the descent is wasted.

I can't speak for the 'c', but for the regular Gen3, 6 out of 8 bars is normal, and probably the highest that flatlanders will see except in very unusual circumstances. For those of us with 500 foot hills, 8 bars is fairly common -- at the bottom of the hills, not the top.

 

um.. yea.. i've gotten the battery full a couple of times...

 

The Prius likes to keep a bit of a buffer, if all the bars are full it will actually increase use of the battery over the ICE till it brings it down a bit.

 

The buffer for regenerative braking energy and the HV battery long life maintenence is a reason. BTW - when you see full bars for State of charge, the battery is not really fully loaded, but just about 80%.

 

Wait until you go down a long steep hill

If you do and the battery goes completely full you'll find the engine appears to rev a little (or a lot depending on the hill). This is normal. The car likes to keep a buffer but if that buffer is filled it then tries to burn off that extra charge to get back into its happy 6/8 zone.

 

You don't want it to be full, and the car will take steps to drain off excess charge, including using the battery to turn the engine.

Never park your car with a full battery either. Always park it with 6 bars or less.

 

Even when the display is 8 bars the battery is not 100% charged
(IIRC = 7 bars =70%, 8 bars = 80% State of Charge).

Even when the display is 0 bars the battery is not 0% charged.
(IIRC = 1 bar = 40%, 0 bar= 30% State of Charge)

The reason the battery is never fully charged is because it would takes too long to do. The battery does not stores power not linearly with time but exponentally with time; i.e. the HV battery initially quickly absorbs an electrical charges up to about 60% of its maximum state of charge rating and then recharges the next 40% of its maximum state of charge rating at slower and later even slower rate as it get closer and closer to 100% state of charge. By the time the battery is 70% recharged - the battery recharging rate has slowed down so slow it become very inefficient to capture any additional charge. The Prius also tries to protect the HV Battery from overcharging pass its 100% rated state of charge because that could shorten the lifespan of the battery as well.

The reason the battery is never allowed to fully discharge is because that would would shorten the lifespan of the battery. The Prius ICE will aggressively recharge the battery when the state of charge is about 40% to prevent the battery from aging prematurely.

The underlying design goal is to extend the lifespan of the battery so it will last over 10 years.

 

yeah 6/8 is normally what mine shows most of the time, I have hit 7 of 8 after some downhill grades, never yet had all 8 lite, so its very normal, but you should see 6 of 8 on a regular basis when not running EV mode.

 

depends on where you drive. Mine got 100% full a couple of times as I descended from mountains

 

Seems fully Charged to me. Only occured during long downhill like GrumpyCabbie state.

 

Last weekend, coming home from the grocery store, I looked at the dash and went OMG because the battery indicator was fully lit. Level roads, no different than the trip I take every weekend. Luckily, I was just reaching the final leg of the drive where the speed limit is slow enough that it burned off the excess in no time. (that was a good OMG, by the way, because just moments before i had been explaining to my passenger that it would probably never show full given the type of driving i do)

 

It's been interesting watching the State of Charge (SoC) reading on the ScanGauge vs the indicator on the dash ... the calibration of the dash indicator is not at all what I had imagined. 60% SoC will appear as six bars and 60% is what the car loves. If you're below ~60%, it will favour charging the HV battery. If you're above ~60% it will favour drawing from the HV battery. If using cruise control at freeway speeds it seems to alternatively charge and discharge the HV battery to maintain roughly around this point.

I've only seen 8/8 bars once since getting the SGII, but it does indicate this well before 80%. Further, on the downward side, the bars drop away much quicker than the %. If you get down to 2/8 bars, it seems to be around the high 30's to 40% and around that point the ICE will come on and force a charge up.

I wouldn't worry about this too much - short version, the car likes 6/8 bars and aims for this point. If you're doing a lot of downhill driving you can end up going up to 8/8 and eventually to the point where the car will throw away energy to protect the battery. If you get down to around 3/8 or 2/8 the car will get grumpy and deliberately run the engine to charge up the battery. Most of the time, there is nothing for you to do here, but you can consider this as a small variable taken into account when adjusting your driving style to the conditions.

 

But you have a Gen 2 and the indicator being "full" on Gen 2 = 75 to 81% SoC (see Prius Palm Mileage Simulator). I've confirmed that via the SoC value I can get via an XGauge on ScanGauge II.

 

Hello friends,
Can anyone tell me the reason why my Prius 3 2010 1.8L does not charge fully now? In fact, previously the battery used to charge fully for the same route I do everyday. I also noticed that when it used to charge completely the engine revolved on its own, like GrumpyCabbie stated. Since about one month, I have noticed that despite taking the same route with the same road conditions the battery lacks one bar to get fully charged. I am a bit worried about this, does this mean that there is a degradation in the Hybrid Battery?
Thanks for your replies

 

how many miles/km on her?

 

The battery indicators are showing normal operation. To test a Prius battery takes something like a TechStream, a Prius-aware diagnostic tool, and operating the car to monitor the module voltages while deep discharging and then recharging the battery. Without the tool and procedure, we can't tell.

Battery failure is detected when one or more of the 38 Gen-1 modules or the current 28 modules has a significant voltage loss showing one of the six cells in each module has failed. The car raises an error indicator and it is time to visit a Toyota dealer or one of the well known, independent Prius shops.

The level indicator really doesn't tell us about the battery health but the degree the car battery is being 'stressed.' If you can drive up hills at speeds that do not pull the level down, you are operating the car in the 'sweet spot.' When descending tall hills, using "B" to minimize overcharging, the most significant stress on the battery, that would be a good thing.

The battery in our Prius is part of the transmission which brilliantly is tuned to keep the engine in the peak, efficiency power range. It allows the engine to be briefly turned off to use previously, efficiently generated energy to maintain speed.

Below 42 mph, our Prius will generate excess energy that it banks in the battery. Then at the earliest opportunity, it turns the engine OFF and keeps the car running on the previously stored energy. It is more efficient to operate the engine in ON/OFF peak engine efficiency than to try and run the engine at a low-power, inefficient power level. Ordinary gas cars throttle back the engine and inefficiently burns fuel to generate low power.

GOOD LUCK!
Bob Wilson

 

Thank you all for your replies. The Prius odometer read around 150,000km.

Can we carry out a survey on PriusChat to get an idea about the odometer reading of all Prius members in the group in the following format.

Prius Model / Year / Country of Manufacture / Milleage Reading (km/milles) / Hybrid Battery status / Remarks

eg:
Prius 4(XW30) / 2010/ Japan/ 150,000km/ Not Tested but Good- No issues till now/ Original OEM Hybrid Battery still my Prius

Thanks in advance for all your replies.