Battery Readings

[micromalc]

Hi,

I recently bought a T spirit, love it, but, I notice that in the "energy screen" the Battery level never goes above about 75%. Is that normal ? Any help much appreciated.

[Rael]

Hi,

I recently bought a T spirit, love it, but, I notice that in the "energy screen" the battery level never goes above about 75%. Is that normal ? Any help much appreciated.

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Hi.... I also have a T Spirit, (and love it!) and have test-driven a couple of others. In my experience it is rare to see a full Battery displayed in most town, and undulating A road driving. In these situations you will see that the hybrid system, when at operating temperature, is constantly drawing from, and topping up the Battery, as required for the most economical results.

Furthermore those who are consciously trying to achieve the best economy will be feathering the throttle to induce the system to use Battery power only, as much as possible, which of course mitigates against seeing the battery full condition.

However when cruising at a fairly constant speed on a dual-carriageway, or motorway the battery reserves are generally not needed so much, and so you should see a full battery indicated from time to time. (The bars on the battery icon turn green.)

Quite often when cruising for a while at 70mph I find that the battery is nearly full for most of the time, and the bars turn green just as I brake at the end of the exit slip road, due to regenerative braking. Then as I pull away onto the ensuing minor road system (completely by battery power only) the bars on the indicator soon turn blue again.

It will be interesting to see if my experiences accord with those of other contributors to this forum.

[Chris Dance]

I agree with Rael's comments.

If you want to see the Battery fully charged then drive in the mountains and use "brake" going downhill. We recently used my sons Prius in the Alps. Battery became fully charged and the engine note changed when the Battery was fully charged. My son came out of "Brake" when this occurred.

For general driving the fully charged condition does not get reached.

I use "brake" when driving down hills etc.

[GreenJuice]

I'm also a proud new owner of a T-Spirit (and wish I'd got one much earlier!).

I agree with Chris and Rael's comments and experiences, and you can find out a lot more information on websites like priuschat.com and cleanmpg.com where there are a large number of postings on all things Prius.

It appears that the on-board computer always tries to get the Battery to an intermediate state of charge (often abbreviated to 'SOC' on websites) of around 60%. There are various reasons for this, including the preservation of Battery life. This means that it will even (occasionally) worsen its management of fuel economy to do so.

One (of several) principles of maximising fuel economy is, paradoxically, to use the Battery as little as possible as energy is wasted in the conversion each time. So striving to keep it in the blue all the time is a technique you might consider experimenting with - smoother accelerations and braking, etc.

Hope you enjoy your Prius as much as I do!

[John in Hay]

Hi,

I recently bought a T spirit, love it, but, I notice that in the "energy screen" the battery level never goes above about 75%. Is that normal ? Any help much appreciated.

Agree with the others - come and drive around the hills of Breconshire and Radnorshire to see a full (tasteful green) Battery !

What I want to know is what happens going downhill once the Battery is full - I presume the energy must be dumped as you still get the braking effect.

[Chris Dance]

Coming home this evening and using "brake" on a steep descent the Battery was showing full charge.

When the Battery is fully charged in "Brake" listen to the engine note change. I take "brake" off when this happens. Perhaps the Prius electric Battery system rejects any more charge when its full??? I do not know for sure just a guess.

[GreenJuice]

Perhaps the Prius electric battery system rejects any more charge when its full???

Yes, I believe your guess is correct. I've found several threads referring to this.

The Battery management tries to keep it at about 5 - 6 bars. Below 4 bars and it will turn on the engine (a.k.a. ICE) more requently to charge it up. Seven and above (bars turn green) and it will try to get it down. I haven't found out exactly how, but possibly by using more hydraulic braking instead of regenerative braking (?). It might also account for the differences in engine noise you hear, as the ICE has to spin at speeds above 41 mph to protect the electric motors and the speed of this may have to vary to satisfy Battery management.

Both 'too high' and 'too low' charge state scenarios result in energy wastage and fuel inefficiency, which is why these 'hypermilers' refer to it as the Prius paradox - the Battery in the hybrid design is what gives you this great fuel efficiency, but in order to maximise this efficiency you have to use it as little as possible!

This link gives a bit more information. Notice that the bars shown on the car's multifunction display (MFD) actually only shows a range of state of charge (SOC) from 40% at 1 bar to 80% at 8 bars (it'll never actually get to 100%).

[GreenJuice]

What I want to know is what happens going downhill once the battery is full - I presume the energy must be dumped as you still get the braking effect.

Here is a thread that explains the 'energy dump' is in the form of spinning the engine and use of the hydraulic friction brakes, both of which result in conversion to heat.

http://priuschat.com/forums/prius-technica...ll-battery.html

Pedal off or braking in B-mode provides some Battery regeneration, but less than when in D-mode. Neither regenerate when the Battery is showing the full 8 bars (80% full). A good explanation is here: http://techno-fandom.org/~hobbit/cars/b-mode.html

[Chris Dance]

When I bought the car the dealer told me to use B for engine braking downhill. That is what I use it for; B use does charge the Battery no doubt about that. As Green Juice has pointed out via his references use B for braking purposes not for charging the Battery. I do not rely on engine braking alone on steep decents foot brakes have to be used as well.

The references given by Green Juice are very good.