How Much Charge Should Battery Take?

The battery should never reach a full state of charge in the Prius. The reason for this is that if the generator (MG2) in the Hybrid system fully charged the battery, then there would be no place to store the re-generated energy when the vehicle was driven. The energy used (fuel burned) to charge the battery would be wasted. The charging system uses an very complex algorithm to determine state of charge based on several factors including voltage rise, cell temperature rise and charging current. I believe about an 85% state of charge is the point at which charging ceases.

 

Oops! I said MG2 is the generator that charges the battery when the engine is running----Should have said MG1. MG2 is the main drive motor while MG1 is the smaller of the two. That's why I am still a Rookie poster

 

The extremes of Minnesota have steep & length decents into valleys. Driving down into them was the only time my 2001 Prius ever exceeded the 3/4 mark.

Dropping to 1/2 from time to time was normal.

Dropping to 1/4 (or lower) never happened.

So what you are seeing is what the system was designed to do for typical use.

 

kenmce,

Here are some real life examples. My first experience with the "battery charge" was at the dealer ship. I was ready to pick up my car, and the sales man said I would have to wait a few more minutes, since they would have to get gas to put in it, and would have to drive it for 30 miles to charge up the batteries. I was shoked, and told him, that I can do that my self, so they deceided to skip that part. Got to the car, and the battery indicator showed half full, not as I expected some where in the read below last mark on the bottom.
My second experience on the "battery charge", was when I was going down hill for several miles and had quite frequently used the "B" mode instead of using the breaks. I observed that the battery charge indicator was filling up the last segment at the top, and all of the sudden I could feel less breaking torque comming from the enigne, and the engine started spinning up to an extreemly high RPM, so I deceided to not continue using the "B" mode / only for the rest of the trip.
I do believe that by design the Toyota concept includes some means of heat - resistive system, why else would the Batteries get so hot that they need external ventilation... Also keep in mind that only 30% or so of the kenitic energy can be recover by means of "regernerative" breaking, so it will take quite a bit of breaking to get the batteries in top charge stage.
So far I have gotten the battery charge indicator from 2 bars above 0 to all bars green, but most of the time I now learned to operate the car so that the battery charge is one or tow bars over the 1/2 mark, during any commute.

Sorry for lengthy reply, but I feel like this can not be explained in enough detail.

Ralph