Why 36kwh batteries, but only 28kwh or 31kwh usable

[Lonwa]

Just curious why we can't use all 36kwh capacity.

Thanks

Lonwa

 

[kish]

There are some nuances, but the bottom line is it's done to increase longevity of the battery.
If it were always charged to 100%, it would not keep it's capacity for as long as if it's charged to 70%-80%.
Same is true for cellphones, but those have shorter lifespan (and some have replaceable batteries) so nobody really cares.

 

[wtzouris]

It's to control how the battery is used. When you deplete a battery to zero or overcharge it to 100% and keep charging it ("boiling" the chemistry) you severely degrade its battery life. Manufacturers need to guarantee the battery performance over the life of the battery warranty. They have figured out that charging to 80-90% and never discharging below 6-10% is the safest way to preserve longevity.

 

[JeffRay]

WTZ, another question for you. What is the small E-cell gauge on the right? It usually shows Max but when I get the battery low warning, it starts to count down to zero. Is that all it does? I assume it has nothing to do with the secondary battery which operates other electronics.

 

[Stretch2727]

The second gauge shows if the power output is being limited for any reason.

Two cases I know this would occur:

-The battery is cold or hot. I think this mainly occurs on startup in cold weather.
-The charge is very low. (Per Jeff's comment the power starts limiting as you approach no charge.)

 

[wtzouris]

Stretch2727 has it right. It is general battery "health" and status. I routinely drive to below 25% and it seems to begin to drop from Max around that point.
In winter if I forget to pre-condition the battery is cold and it is also below Max. I have never over-heated the battery.