what temp should traction battery be during a drive?

Forget the low end of the question. LOW temperatures are NOT a problem. Unless maybe if you live where it gets down to -60 F.

Someone else probably knows the answer on the high side but ambient plus 20 should not be a problem.......as it is hard to control it any closer than that.

 

The benchmark for our (regular) 2010 Prius seemed to be 35C (95F). This was with ScanGauge monitoring the middle sensor (typically a bit warmer) after an extended drive, on cool evening, driving around 80 km/hr.

 

I was using an XGauge, entered into my ScanGuage, and there were XGauges for sensor one through three. Number two sensor is (supposedly) in the middle of the pack, tends to be warmer. Ditto for the central cells. Maybe Prius c has just one sensor though?

 

Does the C actually have active battery "cooling" or is it just ventilation ?

If just air flow, I think you should expect to see the battery temp. just a bit higher than ambient, regardless of what the ambient IS.

 

Ventilation only to keep the battery cool Sam. There is also an HVAC air outlet under the seat which will blow cold air (or hot) towards that hybrid battery fan in the summer when your running the AC.

 

As mentioned there is a middle temp sensor which is best to monitor. The fan is very conservative and you will not hear it speed up until 116f. This is way too hot. This will pass the warranty but not much more then that if you live in hotter climate like So Cal.

As mentioned you can't get too cold unless it way below 32f ambient. I run the fan at speed 6 full speed ALL THE TIME with the scan gauge. Even if it's 50s outside, my bat still gets hot. The worst is when you park and come back, it's way hot. I run the AC down so is uses the duct below the seat. I have seen my temps stay in the 80s-90s this way and it's much better then the 100+ with out running the fan.

 

Can we at least entertain the idea, that a little warm up is maybe not so bad? That Toyota engineers are being diligent?

I'm sceptical, about statements that any raise of battery temp above ambient is terrible. OTOH, I'd agree that "hot soak" seems most detrimental, say parking a hot car in a hot garage on a hot day.

 

Easy rule of thumb given to me by a battery engineer in person: Batteries like the same temps as humans do.

I keep one scangauge on battery temps and it typically reads +/- 10 degrees of ambient but can rise quickly in hot weather with hard use. In NEVER drops quickly; they are a tremendous heatsink. On my Energi with LiOn chemistry, Ford shuts the party down at 113f and only allows hybrid operation as a safeguard but I've never experienced this operation. I've seen higher temps (122-125f) via techstream in my gen 2 NiMH pack while testing it in a summertime garage. I've never seen temp numbers/charts posted here for the NiMH but I know some testing labs have that kind of stuff. FWIW