Why does my battery only charge to 46% in ready mode?

With the possible exception of preserving battery longevity, the car is designed to save gas above all else. I would suspect that charging the battery to a high level becomes an inefficient way of using gas after a certain point. (Something like the law of diminishing marginal returns would probably apply). At the same time, starting the car from 0 rpm to idle speed also uses gas at a faster rate for the brief moment that it takes to spin the engine up to idle speed. The hybrid ECU makes a trade-off between whether to keep the engine running longer and charge the battery less efficiently or stop the engine and start it up again later, with a momentary surge in fuel usage. Apparently this balancing act is affected by the temperature you have chosen for A/C cooling. The lower A/C temperature setting would require more starts within a given period of time, and it is the ECU's judgement that it should run the engine longer to compensate and stretch out the interval between starts.

 

I think that would be part of it. Also, if the outside air is cooler, you could expect to get a longer interval between starts. It might be worth having an A/C mechanic check the efficiency of your A/C system as well (to make sure it has the optimal amount of R134A, etc.) Every 4 to 5 minutes does seem like a short interval, but I'm not really sure what is typical. Hopefully your engine is well tuned, and the motor mounts are not worn, so it can start without disrupting your sleep too much.

 

The computer also wants to keep the gas engine above a certain temperature, because that's a big hammer in reducing overall fuel consumption.

It is keeping that gas engine ready to leap into high power, high efficiency work at the drop of a hat. And that isn't really what you need for your situation.

The engine duty cycle is highly optimized for transportation, and less so for stationary hotel loads. Obviously it works, it just isn't optimized for your usage pattern.

 

The symptoms you describe are often an early warning of a failing HV battery, that is, losing capacity.

Which should not be too surprising for a 12 year old car with almost 200K miles on it.

 

a healthy gen 2 prius runs the engine every few minutes depending on load, and only puts a small charge in the battery. frequent cycling while camping is a common complaint, not a rare one.

a 12 year old battery won't hold the charge as long as a new one.

 

Learn about battery reconditioning... When NiMH get old they lose capacity and you can recover that lost capacity by doing deep discharges and recharges.

 

Yes. That is my "educated" guess.

 

Or you could look up REAL electrical and chemical engineering information about how the batteries REALLY work.......and find out that you can NOT "recover" anything significant by doing ANYTHING once they are worn out.

But some people don't seem to want to hear the truth.

 

Well you see.......the BIG problem with that assumption is:
You don't really KNOW if the "reconditioning" helped any or not.
Maybe if you had done NOTHING, it would be in even better condition.

AND.....that is a rather important piece of information to leave out.
Is there some reason you didn't mention that in your first post ???

 

Educate yourself about the truth Sam:
BU-807: How to Restore Nickel-based Batteries - Battery University

 

I hear ya... If you only got one battery pack and it's in your car and you depend on your car daily, it's next to impossible to find time to get that work done. At this stage it comes down to what your budget allows. Throw $2K at and be done with it as an issue for a decade or spend way less and buy a second pack and rebuild that and then just swap the packs out when problems arise.

 

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