How's this sound. The current Hybrid battery allows the vehicle to travel up to 25-30 miles an hour before the gas engine kicks in. What if the battery was increased in size to twice its current size. Would this allow the vehicle to travel up to 45-50 miles an hour before the gas engine would kick in? The advantage would be going futher with just the battery and better gas mileage overall. If this sounds a bit much, then if you can come up with something better, lets hear it.

It's actually been done before by a few individual folks. I don't have the time at the moment to dig up some links (I will later), but increasing the battery capacity on the Prius increased the range... not the speed threshold. I believe the fuel economy went from about 50 MPG to about 65 or 75 MPG, but the financial cost of the experiment was pretty large.

Visit my newly-acquired website, Volconvo Debate Forums!

I have noticed that when I am on the freeway going 60 just my electric engine will be working until my battery drops to a certain point then the gas engine will kick in again (unless I hit a hill then the gas will come on anyways). This usually only happens when on flat terrain.

Am I misunderstanding this 25-30 miles per hour limit for electric or is my car acting weird?

Let's go with the equivocal "yes and no". The current programming does not allow EV only above 41mph (Prius II)...the ICE will spin up no matter what above that speed. This is mostly to prevent over reving of MG1 (someone correct me if it's MG2).

Using the EV button the top speed is 34mph before EV mode deactivates. This does NOT mean that the ICE will always start up. It's generally been speculated that the reason for the 34mph threshold is b/c of the marked increase in demands on the battery as speed increases as a reasonable cut off point for the battery's capacity.

So, if you increase the battery capacity, under the current programming, there would be no change in top speed for either EV mode or 'Stealth' mode. In theory, however, if you could reprogram the EV mode controls to allow EV at higher speeds the extra battery capacity would be a necessity to make use of that ability. Still, under current design specs (mechanical), You still could not go over 41mph without the ICE spinning up.

As mentioned, those who've added extra battery capacity have significantly increased the range they can travel in electric mode.

Evan E. Fusco, MD
'04 Prius/BC moded to the T
'06 Highlander Hybrid Limited AWD w/NAV

The range on battery is really one of the big dissadvantages to the way Toyota has designed the HSD. Like Evan said, the top speed is mostly limited by the rev. limit of the MG1 (the one on the sun gear). Also, the MG2 looses effiency the faster the car is traveling (electrics like low revs, high torque).

Hidden Views Photography