is the heat killing my battery?

How old is your 12v bsttery? Have you checked the volt readings with the on-board method found here? Weird stuff happening? MPGs dropping? Test The Battery | PriusChat Report all three values back here.

 

Just continue to use the AC to keep you and your HV battery cool even though it does lower your MPG in hot weather. Check that the HV battery vent is clear and it's a good idea to clean out any lint that may be blocking the air flow. If you are concerned about the state of your HV battery, there is a low cost ($50) data logger that you can use to get data that will indicate the battery's state-of-health,

Traction Battery Health Monitor for Toyota Prius - OpenElectrons.com

Then upload the data file from a trip and we can analyze it for you.

JeffD

 

Please fill out the questionnaire that is in the link below and post the results back here so all of us can read your answers. Only then can we truly asses if you do indeed have a problem.

Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

 

Once you know that the 12v is OK, a tell-tale sign of impending traction battery failure is seeing unexpected cycling of the battery SOC in steady state driving.

To wit: Go out for a highway drive on a flat road at 65 - 75 mph. After a couple of minutes the battery icon should settle down to 5-6 bars.

 

Are you just starting to use the AC? The AC compressor will increase the power draw by 2 to 3 times the usual with no arrows on the screen/stopped at a light with ICE off. That can leave it playing catch-up after a long stop or glide.

 

Yep riffinator, this is most likely all that your problem is. Using the aircon generally sucks down the state of charge a little (or a lot in the case of frequent stopping). And when the SOC is low then engine works a bit harder to make it up.

Keep using the aircon however, as you need to keep the cabin cool in order to also keep the traction battery cool. You could try a slightly lower power (higher temperature) setting if you like. Remember that you can adjust both the temperature and the fan speed.

 

The A/C is electric, so it's probably draining your traction battery. When the battery gets low (3 bars I think) the ICE automatically kicks in until the battery is restored to 4+ bars. This happened to me when I was visiting Arkansas and there were too many hills. Back in the flatland of southwestern Tennessee, I've retained about 49.7 MPG average in this summer on 95 degree days. Remember to keep accessory usage down like:

1. Headlights. ONLY use them when you need them. Don't be some fool who leaves them on all the time because they are a big energy culprit.

2. Stereo. Some people will exaggerate the energy usage of the stereo, but the truth is that if you turn it up loud then you will be sucking energy.

3. Air conditioner. Please oh please don't be one of those people that blows their A/C at 65 degrees constantly, no matter what fan speed. For many people, setting the A/C to 75 degrees on automatic mode is quite comfortable enough. The colder the A/C has to make the air, the harder is has to work, EVEN ON LOW FAN SPEEDS.