Remaining battery gauge vs. EV range - does not really make sense

The car's battery management system, aka silent HAL, will prevent your battery from fully discharging to protect it so you'll always have a couple bars then it switches from EV to HV (ICE).

 

Most of us have found the lowest reading to be two bars. We are sure this is controlled by the car so the battery can not be fully discharged; a process that is known to damage Li Ion batteries. Funny Honda didn't do the same thing on the top end and the car can charge so the gauge shows full. But we are certain that a 100% shown on the display is not 100% battery charge for the same reason; Li Ion batteries life is shortened by full charges.

Pretty much all electric cars behave the same way.

I've found both the EV graph and the Gas graph on the other side to be pretty good instruments for knowing the remaining power stored for use. The gas gauge has 20 bars and I can usually fairly well predict how many gallons I'll be able to put in the tank by looking at the gauge.

 

Are you suggesting Honda should have left the top two segments permanently dark and a "full charge" would not go to the top of the gauge? That would mean that the top 2 and bottom 2 bars are robbing the gauge of more meaningful resolution.

In my opinion, Honda should have not used up the bottom two bars to represent the buffer protecting the battery from becoming completely discharged. The gas gauge can go to zero; the battery-charge gauge should do so, too. Why limit the resolution of the battery-charge gauge by keeping the bottom two bars always lit?

 

I agree. The bottom two segments should not be left permanently on. The gauge should represent usable capacity only.

 

Yep its super confusing, especially for new owners and dealerships since the drive is completely different when battery is drained, but the people driving it won't realize that the battery is dead since it shows two bars and will think it just drives poorly.

 

If I had my way the bottom two bars would not be shown.

 

I could be wrong, but I think there are two low end buffers. One at the bottom end is simply to keep the battery from fully discharging and thus extend the life of the battery. But I think there is a low-end operational buffer that allows the battery to enable some limited hybrid-vehicle behavior. Not for long climbs up hills, but enough to supplement the ICE and improve the efficiency. It is my belief that this HV buffer is the two-bar buffer that we see on the gauge. I believe the bottom-end battery protection buffer is unseen, like the top end protection buffer.

 

How do we know that a "full" battery gauge doesn't mean that the battery is actually only 90% full and Honda has the gauge show "full" just to please the us?

 

This would be interesting to test out but how??

 

@V8Power , I did a limited real world test by allowing my EV to go to 0 and 2 bars until it auto entered HV (it was hard to do as I suffer from IAS [ICE Anxiety Syndrome]).
In 20 miles of mixed city and highway driving with speeds of 35 and 55 and no large hills, everything was fine. The 2 bars never increased and I had no loss of power or high reving although I suspect that on a large enough hill I would have. I could not force myself to test longer, but I suspect that you get a little lower MPG since this limits the full range of power flows the algorithm can select from. This observation might support @Ray B ‘s theory that even at the 2 bar buffer limit, the algorithm allows a small amount of back and forth charge/discharge but not as much as in a normal/larger SOC and thus you get the angry bees when calling for more than just limited amounts of power for short durations.

As to the buffer question. We have several observations that with a fully depleted battery (0 EV, 2 bars) only 14.1 to 14.4 kW could be added to the state of charge (SOC). So 14.4/ 7kW = 83 to 85% of the battery is allowed to be usable. So we assume that 15 to 17% is the total buffer but we don’t know how it’s apportioned between top and bottom. But one also has to take into consideration that the charging inverter in the car cannot be 100% efficient and so not all of that 14.1 to 14.4 kW actually makes it to the battery pack. You can’t beat the laws of thermodynamics and so some of the kWs measured at the wall by your EVSE or Killa-Watt meter are lost to inefficiency as heat in the car’s charging inverter. I’ve seen estimates of inefficiency anywhere from 20 to 5% and speculation that Level 2 charges may be more efficient than Level 1. If you assume a around a 90% efficiency, then only 12.5 to 13 kW are allowed to be used. Then that’s a total buffer of 23.5 to 26.5. Holding about 25% of the battery capacity in reserve for battery protection and to mask the unavoidable degradation from the consumer is roughly on par with other EVs and is another indication that our assumptions and speculations are at least in the ball park. Again, what we don’t know is how this assumed, appropriately 25% buffer is split between the top and bottom of the SOC.
Also common sense informs us there must be buffers at top and bottoms since every other large Li-ion battery pack has this and the chemistry/physics dictates that repeated full 100% charge and 100% discharge cycles will destroy any current Li-ion battery no matter what the chemistry or configuration.

Fortunately we have some very intelligent people on the forum and as we build up more observations for them to chew on, we will be able to peel back more of the onion of mystery surrounding our Claritys. Oh what I wouldn’t give to be able to button hole a bunch of Honda engineers and software developers in a locked room for a day!

 

Here's a short version of what Ken wrote: the rated sizes the battery is 17 kWh. When the car has 0 EV range and you plug it in to charge, the car will only actually take about 13 kWh. So there's 4 KWh that can be used as a buffer. They are designed to not use up the whole capacity of the battery to have less battery degradation.

 

I understand that. I agree that there is probably a buffer on both sides of the battery (empty and full) to extend battery life. I'm just saying that unlike the bottom side of the gauge with the 2 bar 'buffer', I think they let the meter go all the way up to the top and show 'full' so customers would not freak out about not being able to get the meter all the way full. Imagine the hysteria if we could only ever get 2 bars short of a full meter!

 

The ICE is small, so some battery power must be reserved for performance.

Why not set this level to 0 bars? It's useful to know how much of this reserve is remaining. Just my theory.

 

Because who ever designed it is dumb. I agree don't show 2 bars when there's no usable EV, show 0 bars. Anyone know of any other PHEVs that does this? I know my Prime doesn't.

 

Agreed. If they're going to let us get to a full meter when the battery isn't actually at 100% then they should have done the same for the other end of the meter. I imagine this is something they could correct with a software update.

 

I think the reason is to show you that the car is now functioning as a hybrid. If it showed zero EV it would imply the car is running only on its tiny motor. Its a good thing that does not happen.

 

100% bars = 100% of desired charge
You can always add more electrons until bad things happen, so every manufacturer has to answer the question "100% of what."

 

This does actually bother me on the infotainment screen that shows the car and charge levels, because it does "max" out at like 75% on the left bar and the gas goes all the way to the top on the right side.

 

I believe that when you get to 0 charge/2 bars, you ARE running on engine power alone, not hybrid power.