Why is my battery never full or empty?

My understanding is that Toyota designed the gauge to read that way, and the system to work in that manner.

In other words...even if you do reach "full"...the battery is not really full...and conversely it's never really as low as it may look.

My understanding is battery charge management in The Prius is designed to maintain a "middle way"...and this promotes a longer battery life.

Exactly why maintaining this constant middle ground is best? Well, I'm sure I've been told, but I can't remember. I'll rely on the Prius geniuses for that specific.

But in short, the behavior you are witnessing is the norm, and it is by design.

I rarely reach a gauge reading full charge...usually only if I'm going down a long hill or mountain. It happens occasionally but the "average" norm for me is a battery gauge reading 1-2 clicks from the top.

 

Simply put Prius chemestry batteries last longer when their juice is primarily stored in the middle .... that way they last longer. Thus, the software will try to accommodate that area. Fact is there's even more capacity above and below what your little display even shows - but your Prius never was designed to ever get access to the top or bottom end of the battery's capacity
.

 

The key here is that it's not a battery powered car. The battery and motor are just there to enhance the throttle response of your very economical but nominally sluggish engine and to easily start it up quietly and frequently.

 

If you view the battery as a power reservoir, you never want it full or empty.

When it is empty (in the opinion of the computers) you are left with the wimpy engine. (73 HP vs 110 HP combined)

When it is full (in the opinion of the computers) you can no longer do regenerative braking. (you still have engine braking and friction braking, but both waste 100% of the energy)

Edit: spelling error, as pointed out below

 

Well since you have regenerative brakes...pressing the brakes occasionally as you are going downhill would actually add more charge.

It is a little strange if you can't get the gauge to read full even if going down a down hill stretch. Usually I can in those situations.

But I'm looking at your join date and assuming you simply haven't owned the vehicle that long.

If your gas mileage is acceptable and the operation of the vehicle on all other fronts is normal, I really don't think you have anything to worry about here. "Full Gauge" should happen someday...next time you are coasting down hill, as you gain speed..try SAFELY braking a little, within the charge limits.

I have about a 2 mile down hill stretch that I occasionally have to take. That is about the only time I do reach full charge.


Hey! Toyota 100% denies any reports of The Prius having "fiction" braking.

That was all taken care of with the software update...and the carpet mat tie downs....

 

there are 2 mile hills, and then there are 2 mile hills. around here, a 2 mile hill won't come close to filling the battery. but as usual, we don't know where the o/p lives or what the topography is like.

 

Not too surprising since regen braking doesn't kick in much or at all until you lightly push the brake pedal.

 

I think the "battery gauge" is calibrated differently in the C.........so that it accurately shows the entire capacity and that you are only using the center 70% or so.

I believe other models are calibrated so that full =75% and empty = 15% (numbers are guesses).

 

Mine is often full. Then again, I live in a mountainous area.

 

Well I admit my knowledge of the battery capacity of the Prius being calibrated to embrace a "middle way" of charge and discharge comes from the standard Prius.

It wouldn't surprise me at all, if just based on size and weight that The Prius C is calibrated differently. I would think on one level it would almost have to be.

 

Except the computer doesn't allow the battery to explore those limits anyway, for the sake of battery health. The state of charge will not go over 80%. It just won't. As you approach 80%, the computer will start turning the ICE to use up excess energy and if you do make it to 80%, the computer ramps this up. The ICE can in fact get really really noisy if you're coming down a decent enough mountain pass and are attempting to do it on the regen range alone. The car does what it has to do to keep the battery to a maximum of 80%.

What you're really referring to here is the fact that the computer tries to keep the battery towards 60% state of charge, all other things being equal, so that it has room to move up and down from there.

It's not that hard to see all 8 bars of the battery display lit up, but you will need a decent descent to do it (and then it's almost impossible not to do it). In regular city or freeway driving, you will not see all 8 bars fill up, due to the car's tendency towards 60% charge.

There's some good discussion and a nice graph over in this thread: Low Battery engine behaviour | PriusChat

 

I see he missed the "In the opinion of the computers" part entirely.

 

How much elevation change in that 2 miles? For that distance, it will need typically 400 to 600 feet of descent to fill the battery, depending on speed and amount of braking.

If the hill is shallow enough to not need any braking, it will need more elevation change and far greater distance for the 'synthetic engine drag' regeneration to fill it up.

 

I felt this point was causing confusion to people (or more to the point it regularly confuses people and leads to this being a FAQ) and deserved to be explained in greater detail. YMMV.

 

Ive had a full charge twice when going down the mountain roads. I guess alot of energy was wasted since they were full long before I got down the mountain. Ive never dropped below two bars before the ICE turns on