Is there a proper battery operating temperature?

Our third gen settles in around 35C. And this is in cool evening temps, easy driving around 80 kmh.

 

I suspect it isn't all about the battery, but rather getting the ICE up to optimum operating temperature.

 

You'll need to get a 3rd party solution. I personally like to use my old school scangauge II but others prefer to use an OBD wireless transmitter to a bluetooth device (phone/tablet) and use an app like Torque. The latter solution is cheaper but more cumbersome to use IMO. I have both.

 

Yeah ScanGuage. I've disconnected it now, might have been causing a communication issue, weighing on the OBD port all the time. This was a stab-in-the-dark by a mechanic doing diagnostics when we were having brake communication issues, but it might be true: no return of the problem post-Scangauge, so I'm going with it for now. But yeah: I had battery sensor #2 (the middle sensor, typically the hottest) routinely displayed, and on cool evenings driving a coastal highway back home, around 35C is what I'd see a lot. Going from fuzzy memory: battery fan speed would be either off or 1 (out of a scale of 5 or 6?).

 

As far as I know it doesn't do anything specifically to warm up the battery. However, a cold battery is not as efficient, and in particular regen is limited based on battery temperature. Normally on the Scangauge I see 80-100 amps of regen when the battery is at 90-100F. Somewhere in that range the battery fan kicks in and I've only seen it go over 100F either after sitting in the sun all day, or when driving down a long hill and maxing out the charge.

This morning the battery was <40F to start and I was lucky to get 50 amps of regen.

What limits the battery is its ability to re-combine hydrogen that's generated during charging. There is always some amount of hydrogen generated during charging due to electrolysis, and when the battery is cold it's not as able to re-combine it with oxygen. This production of hydrogen and re-combining is one of the reasons the battery is not 100% efficient, and is partly why the battery warms up under charge.

It's a bit ironic really. The way to warm up the battery (short of having a separate heater) is to put as much charge through it as possible, but a cold battery can't accept charge as fast as one that's already warm.

Note that this applies to both NiMH and LIon chemistries.

 

I observed the same thing. On highway speed the BT2 will settle at 95~ degree F.

But if i drive more local the battery will continue to heat up to up to 103 F. Then the battery fan will prevent it from going higher. It is still possible to go even higher if i have tons of regen.

 

Are you certain that Li I gives of hydrogen?

 

I believe they don't. Lead-acid batteries gave off hydrogen which was potentially explosive if not vented properly.

 

That's exactly what I thought, but admit I'm no expert. Thanks Alan.

 

I've learned not to trust Dr GOOGLE. But I did check with the Dr, who seemed to indicate that Ni-MH batteries do, but not Li-ION.

 

I'm 99% certain they give off something, though it may not be hydrogen. The reason is coulombic efficiency. If you put 1 amp-hour (ah) into a battery during charge, you'll only get some fraction of it back, say 0.99 ah if the battery has 99% coulombic efficiency. Note that this does not include further inefficiencies due to resistance that cause the charge voltage to be higher than the discharge voltage.

So what happened to the other 0.01 ah of current that was put into the battery? In an old fashioned lead-acid battery, it was used to split the water molecules in the water-based electrolyte into hydrogen and oxygen, which if the battery was really old fashioned was vented to the atmosphere and thus the need to periodically add water to the battery. In a more modern, sealed battery they are re-combined internally and thus no gas is actually vented to the atmosphere.

If a lead-acid battery is left on charge indefinitely, as it approaches full capacity a larger and larger portion of the current will result in electrolysis instead of actually charging the battery.

In a Li-Ion battery, which has high but not 100% coulombic efficiency, I still believe that the inefficiency is caused by a similar chemical reaction in the electrolyte. I couldn't find anything definitive in a web search, but did find this link that was studying the effect of an electrolyte additive: http://jes.ecsdl.org/content/153/6/A1031.full.pdf, which contains paragraphs such as this:

The oxidation of LixCoO2 stops at the state of charge of the battery with the additives during charging, and oxidants are produced by another reaction. The oxidants move to the negative electrode and oxidize the negative material, which consumes the charge energy and causes a species shuttle. This reaction process is a phenomenon that appears similar to the “gas recombination” or the “oxygen cycle” of sealed-type lead-acid, Ni–Cd, and Ni-MH batteries.
​

Elsewhere in that article there's an interesting note that with the additive, gas generation is reduced but the temperature of the cell increases faster and sooner during overcharge. More evidence that the "lost" charge energy has to go somewhere.

 

The WIKIPEDIA article " Lithium-ion battery - Wikipedia " has a good description of Li-ION batteries explaining the formulas (under the sub-heading "Electrochemistry"). Not sure of the chemistry - while it's an interest of mine, my last formal chemistry education and dabbling with formulas etc was about 45 yrs ago.

It's probably not possible to know exactly the formulation of a TOYOTA Prius Li-ION Battery, as there are many formulations. On 30 October, Reuters reported regarding TOYOTA (there was a photo of a PRIME):
"Engineers at Toyota Motor Corp say they have tamed volatile lithium-ion battery technology,
and can now safely pack more power at no significant extra cost, giving the Japanese automaker
the option to enter the growing all-electric car market."

[ full article here: Warming to lithium-ion, Toyota charges up its battery options| Reuters ]

 

Aqueous batteries like lead acid and NiMH can produce hydrogen and oxygen as electrolysis products of water. Lithium ion uses a lithiated organic solvent which doesn't decompose. The small lose in coulombic efficiency goes into repairing the SEI (Solvent Electrolyte Interface).

 

I noticed that article also said that Toyota does not currently have a battery powered EV.
The Toyota Prius is just a myth. Time to call Mythbusters!

 

I guess technically, PRIUS isn't an EV, but a hybrid - as it primarily is driven by the ICE, with the EV mode supplementing drive.

 

My Prius is definitely battery powered and I did not get the hamster powered battery option so it must be electric.

 

No hamsters here, either.

But, I must check - mine told me to add fuel/petrol/gasoline yesterday. Maybe I should have ignored it to see how it went.

Seriously, I think Gen 3 the ICE provided 73KW and the BATTERY powered Motor only 27KW (a little different in Gen 4). That 27KW is fairly limited with how far/fast it will get you. I tried mine the other day when there were no cars on the road, it went just over 1km, though the first 100 metres was up a gentle incline. It may go a little further on dead level ground, but wouldn't have got me any further without the ICE.

 

Jetlash1000 did a review on U tube on distance travelled in EV mode if you're interested.