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Hybrid Battery Temperature

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Now that the weather is warmer, Hybrid Assistant is showing my hybrid Battery tempurature as getting up to 45 degrees.  The fan is then running at level 3. 

I've cleaned what little fluff was on the 3 vent grills under the rear seat, but even if I set the fan manually to level 6, not that much air seems to be sucked into the vents.

So, four questions.  Is 45 degrees something to worry about (today was about 30 degrees here in France and the drive was about 90km on open roads); secondly, is the Battery cooling fan likely to be clogged; is it easy to get to for cleaning without having to worry about high battery voltages on potentially exposed wiring under the back seat and lastly where is the hot air from the Battery cooling system exhausted out of the car (maybe the outlet is blocked)?

I have no fault codes or error messages, touch wood, and the engine was running at 86 degrees.  Yes, I know that that info is not particularly relevant.

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You can let sytem decide proper vent speed, but it may be a useful help to have air conditioner ON  for Battery and your wellness 😉

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When you say you cleaned the vents/filters under the rear seat did you actually remove them and do this?

From what I have read 40-60 degrees is normal operating temperature, obviously everything is computer controlled so if the temperature did exceed the safe level I feel you would get a warning for check hybrid system and a code.

There are 3 fans located within the Battery pack so some dismantling to get to them for cleaning plus the HV danger aspect of the job.



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Hi Steve,

Yes, I took them off, but there was hardly any "lint" on any of them, or in the vents themselves (as far as I know, the car has not really had many rear seat passengers in its life). Funnily enough, I went out in the car last night when it was 15 degrees outside, and the temp went up to 44 after about 10km (showing red on Hybrid Assistant).  After we came out from the restaurant and drove for a couple of km towards home, fan still on 3, the temp went down to 39 quite quickly and then up to 40 (yellow on HA) - where it stayed.

According to HA, the batteries seem to retain heat for quite a while when the car is turned off.  They are quite dense, I suppose.

I've got the manual for the car, so the next stage was going to be having a look at the fans, but as you say, if something was wrong in that area, there would certainly be a warning light flashing somewhere.

Could I ask where you read that 40-60 is the normal operating temperature for the batteries?

It could be that HA is "calibrated" a bit wrong for the car, and 44 degrees is actually a normal state and should be shown as green rather than red.

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1 hour ago, Superduner said:

It could be that HA is "calibrated" a bit wrong for the car, and 44 degrees is actually a normal state and should be shown as green rather than red.

I'm not sure that the colour coding is necessarily accurate for all car models. I've noticed that the colour is not really a useful guide on the IS300h for all circumstances. For example, if you set cruise control at 70mph the state of charge shown on Hybrid Assistant is continuously spot on 60%. Hybrid Assistant is set to regard this as good and shows it as green. But if you park the car in Ready mode, the Battery will consistently run down to 40%, then it starts the engine to raise the charge to 50% and then stops the engine. I can't remember if 50% is green, but I'm pretty certain all the 40s are shown as yellow and then red when you get down to 40%. But this is normal operation. The car always does this, so it seems to me that a warning colour is not warranted. The car wants to run the charge down to 40% before starting the engine. This is normal.

As for the Battery temperature, I haven't paid a lot of attention to the colour. The temperature to the left of the Battery temperature is the intake cooling air temperature. Is this a lot different from the outside temperature? On the IS300h the intake vent is in the cabin, so you might expect the intake air to be a similar temperature to the cabin temperature.

Have you tried using Hybrid Reporter to look at data from earlier trips? This used to be a separate app but I think is now integrated into Hybrid Assistant. You could check if the Battery is always 15 degrees higher than outside temperature. I've had a look at an old journey that I have stored and on a one hour journey cruising at 70mph the Battery started at 35C and after an hour had risen to 39C. But the outside temperature was around 20, so the conditions were cooler than in France. Also the Battery would, I imagine, have little use when on cruise control at 70 mph. It discharges a little bit then recharges a little bit. I would guess these minimal adjustments don't have a big impact on its temperature. In hilly terrain in hot weather, I imagine the Battery would get a lot more use and reach higher temperatures.

One other thought. If the fan is at setting 3 that suggests the car computer is happy with the temperature, assuming it can go up to 6 if necessary as on the IS300h. You already know you can increase the fan speed by tapping the fan symbol on the HA display. Although you can't feel much effect on the air flow, does the Battery temperature change if you leave it on 6 for a while?

Here's a 10-year-old Prius thread which suggests near the end a maximum 55C for the Battery for cars at that time.

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