Leaving Prius 2007 idle for six months

I still say charging the battery above what it normally keeps it at is superfluous and unnecessary, and more likely to be bad for the battery than good for it.

 

Hi Ed,

On a conventional vehicle, when the gear selector is in D and the brake pedal and accelerator pedal are simultaneously applied, the car feels like it is trying to surge forward. This is because the friction brakes are holding the car in place while the gasoline motor/transmission are trying to move the car forward.

If you were to actually try my suggested method on Prius, you would find that there is no loading on the friction brakes while the brake pedal is depressed, which is another way to demonstrate that MG2 is not being powered while the brake pedal is applied. John (Britprius) addressed this topic in this thread from the point of view of what diagnostic instrumentation would show.

If an individual driver is incapable of simultaneously applying the brake pedal and accelerator pedal, that is OK, that individual needs to understand his limits. However I would contend such a driver should seriously consider selling his car and cutting up his driver's license as much more difficult driving challenges will appear occasionally during the daily course of driving, and one's ability to respond correctly is the difference between being part of an accident or not.

If you have the engine operating at idle speed, it will take a very long time to make any change in the traction battery SOC gauge - try it and see. My suggested force charge method results in the engine operating at a faster speed when the traction battery SOC is low, while the engine RPM automatically slows down as the traction battery SOC approaches 7-8 green bars.

Hi Daniel,

When driving downhill (60 mph or so) on mountainous terrain after a prolonged uphill climb which has depleted the traction battery SOC, I find that my traction battery SOC moves from 1 pink bar to 8 green bars in a matter of several minutes - which is much faster than the force-charge method will achieve. So from the traction battery's point of view, force charging is no worse than mountainous terrain driving which the car must expect to encounter from time to time.

Again, I don't recommend force charging as a daily activity, but only in the case of the OP who wanted to store his car for 6 months undisturbed. Toyota's own recommendation is that the car should be made READY 30 minutes at a time, every two months, to charge the traction battery. Therefore I disagree with your suggestion that an attempt to bring up the traction battery SOC to the high end of the allowable range prior to storage is "superfluous and unnecessary."

 

There is one other time that force charging can be useful. This is if you park on a steep incline facing down hill "perhaps driveway" something that really should be avoided in the Prius.
When you go to reverse with a low HV battery the car may not move and starts the ICE. This makes it even harder to move backwards as the ICE while using MG1 to provide electric power tries to drive the car forwards while MG2 tries to drive it in reverse. Force charging the battery for a few minutes will allow the car to just use MG2 for reverse movement without the ICE running.
This happened to my while on holiday in Cornwall, coming down a narrow coast road (8ft 6inches wide) and incline of one in three, to find the road blocked by an accident. Had to reverse half a mile back up the hill stopping twice to recharge. Car was loaded with 4 adults and luggage for two weeks holiday.

John (Britprius)