Fitting mobility 12volt AGM battery.

Ordinarily, if I have managed to work a question down to only one option I can't exclude, it's time to take the next question.

 

Post #9 by BritPrius himself discusses various post attachment options, and option #3 is the easy peasy, no extra parts required, method I used. This requires buying a battery with female threaded posts. I am not sure if they all use the same size threads but the mighty Max battery which I used and posted the link to definitely uses the right size. I literally just threw some Toyota pieces to the side and bolted down directly to the battery.
I will attempt to add some pics- the terminal posts, and the baggy shows the parts I had left over, stashed to the side of the battery in case of ever needing to install a stock 12 volt.

 

I appreciate the kind words but as I reread what I wrote I'm dissatisfied with the language I chose. I could see how by using definitives, some enthusiasm that could be perceived as arrogance is on display, and I'm definitely no expert about this, I'm a tinker playing around.
I didn't mean to be dismissive, but rather enthusiastic, by saying "read the thread," this entire thread is a worthy and hardy read.
Hats off to all those before me, particularly BritPrim.

 

I'm very pleased with the language you chose... I'm fed up with the the fear & loathing attitudes that play right into hand of paying triple the cost when that's not needed.

 

That's funny. This eBay listing shows no indication of this item being intended or suitable for wheelchairs, mobility devices, or medical applications or environments. Or even meeting any particular standards whatsoever.

It does have a generic CE mark. OSHA says of this:

"The CE mark is unrelated to the requirements for product safety in the United States. It is a generic mark used in the European Union (EU) to indicate that a manufacturer has declared that the product meets regulatory requirements in the EU that may or may not include product safety. In the United States, under OSHA's NRTL requirements, the product must have the specific mark of one of the NRTLs recognized to test and certify this type of product."

Looking around, the first standard I find for electric wheelchairs appears to be ISO 7176-25: 2013 -- "Batteries and chargers for powered wheelchairs." Unfortunately, it is pay-walled behind a triple-digit price, and I don't have workplace access to it. So perhaps you could copy us the relevant portions of this or whatever other regulatory standard you are using. Then we can explore further to see if the Prius 12V system meets the battery charger portion of said standard when used with a conforming battery of this type and size.

 

All this effort when it comes to risk & you probably don't even like having to wear a mask as often as needed? This thread was started of the wise words @Britprius who lives his life in a wheelchair. He'd have far more to say about what he thinks about an able bodied person's rendition of wheelchair battery certifications. I'll message him an find out if he's still about...

 

No need to pull him back in, he already pointed to a product page showing far more usage information and certifications than that uncertified mystery eBay item you linked:

https://www.ritarpower.com/uploads/ueditor/spec/RA12-55.pdf

 

The issue is you can't buy those in the USA as I recall. That product has a vent tube iirc.
Here's what they're calling its replacement, I don't see certifications, no vent tube.
So the questions are, does it ever outgass? Is the hybrid battery airflow in the battery compartment sufficient to exhaust any possible gases should they exist?

It stands to reason these batteries that can be mounted in any direction are pretty sealed up and would exhaust only under extreme circumstances.
It also stands to reason that any battery like this will eventually emit gases, in extreme circumstances, prior to exploding.

These are logical and sound questions, let's continue the lively discourse with mutual respect!
12 Volt 35 AH SLA Internal Thread Battery – MightyMaxBattery

 

I'm well aware that these cases are rare, enough so that numerous people are willing to take this risk. That is their prerogative. But hand-waving this risk completely away as just BS, nonexistent, in front of novice owners, without adequate support, is irresponsible.

None of the safety and compliance engineers I worked with ever took such a narrow and dismissive view of potential faults, where all the failure elements are well documented in related fields and products.

It isn't good enough to point to a lack of notice of a particular fault in a particular model. Specific and documented technical reasons are needed to show why such faults in related analogous situations won't occur in the new situation we are creating. Such remains absent from this discussion.

As for Prius never showing more than "~14V", that might be true in Gen2, but is a bit of a lowball for Gen3. Here is mine during a normal warmup, before it steps down as battery charge rises:

I always suspected that my ScanGauge installation was reading slightly lower than the true bus voltage, this proved it:

[brightness and contrast adjusted]

Note that these voltages reach into the range where, if the charging profile stepdown and temperature compensation should fail, some makes / models of VRLA batteries can experience thermal runaway at temperatures some hot climate owners will experience during summer parkinglot heat soaks. See the papers linked at the bottom of this post.

How so? My understanding has been that motor vehicle charging system faults can deliver substantially greater overcurrents than can common charger bricks plugged into standard 120VAC circuits.

E.g. my quick survey of available mobility chargers saw a population all rated at or below 10 amps. Automobile 12V systems normally are north of 75 amps, the Prius is built for more than 100 amps. When faulted, those higher capacity automotive systems can generally deliver higher currents.

If you have contrary information, please bring it forward and educate us.

Is that your threshold for action? If so, then all of my household's vehicle recalls, ever, were invalid. Even the Takata Airbag issue.

A large majority of our recalls involved zero fatalities, just a potential for such based on analogies to other equipment.

While we have only a single identified H2S incident in a battery-in-cabin passenger vehicle, we have more such evidence from battery charging faults in other settings, e.g. industrial facilities, forklift operations, and recreational boating. While these are not anywhere near the top of the list of H2S incident causes, they do happen.

It is a very good thing that you don't work in commercial airworthiness certification, it wouldn't be healthy for any of us.

This isn't about just batteries, it is also about the chargers applied to them, generally not in use when the rider's butt is parked atop them at common room temperatures. You are avoiding this angle. The Prius charging system is not regulated by those extra-stringent medical standards and regulations you allude to.

It also doesn't help that those eBay batteries you pointed to, are not labeled or claimed as meeting any medical or mobility standards, or any meaningful standards whatsoever.

I have already asked for what regulatory standard(s) you are using for mobility batteries and chargers, e.g. ISO 7176-25: 2013 -- "Batteries and chargers for powered wheelchairs." No response so far, and I don't have affordable access to that pay-walled ISO content.



For readers interested in learning more detail about thermal runaway in these batteries and about how close our 12V might be to this issue, here are two papers I found. This is a much greater issue in sealed AGM and Gel batteries than in wet types (used under the hood, not in cabin) that are meant to vent their produced O2 and H2. H2S emissions would occur in some, not all thermal runaways.

The first indicates that runaway can start real close to my Gen3's initial charging voltage, though only if that is sustained or exceeded (e.g. by a charger fault) at an ambient temperature more likely found in a hot climate after a long heat soak in a blazing hot parking lot, not in a human-occupied hospital room.

The second describes testing that found great variability: "This clearly showed that not all VRLA batteries are created equally. In conditions that cause one manufacturer’s battery to go into thermal runaway, another manufacturer’s will remain stable. " While the better models had wide margin, some weaker models actually did enter thermal runaway at the voltage I pictured above, at temperatures one would expect in summer climates, one even starting within ordinary driving times. It shouldn't actually initiate if the Prius' 12V system properly steps down to normal float voltages as the battery charge rises and temperature compensation works correctly, but could become vulnerable during a fault. Initial runaway near threshold conditions will likely progress very slowly, likely not becoming consequential in 4-5 hour drives. But with weaker makes or units, fault tolerance margins will be getting skinny.

Both also point to internally shorted cells contributing to thermal runaways in otherwise non-runaway conditions. The testing in the later paper actually encountered shorted cells.

TECHNICAL BULLETIN 41-7944 Runaway in VRLA Batteries - It's Cause and Prevention
https://www.cdtechno.com/pdf/ref/41_7944_0712.pdf

NEW INSIGHTS INTO THERMAL RUNAWAY OF VALVE REGULATED LEAD-ACID BATTERIES
https://www.sbsbattery.com/PDFs/VRLAThermRunawayStorageBatterySystems.pdf

 

Wow... Why is this so important to you? It's like you wrote a whole book for no one but yourself... @ConcreteJimmy and I and others are not going to be convinced. You're splitting hairs here to prove a hypothetical point, hide behind certification claims from other countries, scientific papers rather than actual documentation of failed batteries in real life, etc. to prove something that is perfectly safe is not safe. It makes no sense?

And by the way, when I use "~" I was using a symbol that means roughly 14v or ~14v.

I'm embarrassed for you that you'd argue that 14.7v is different in any way than ~14v... I mean don't you have more important things to do?

 

Readers will note the significance of this difference when looking at Figure 12 of the second paper (and note that the authors tested 24V batteries, not 12V, so scale accordingly).

At 14.0V (equivalent), none of the tested batteries initiated thermal runaway under the explored conditions. But at the higher voltage I pictured from my Prius, two of the four battery models did enter thermal runaway. And did so a half dozen times among the various test runs.

If going this not-risk-free route, battery quality will be important. Beware when trading off between quality vs price. Many lower priced batteries are not marked or claimed to meet any relevant regulatory standards.

 

All good then! ;-)

 

Those images are too small to read... What's your point? Something about a voltage calculation to avoid over-charging?

 

That is a good start. But don't stop there, keep reading.

Let's start with that M55-12 SLD M-series battery. Notice that that 15.0V maximum charging voltage is at a temperature of 25℃, and is linked to a temperature coefficient of -5.m/℃/cell. Also note the maximum charging temperature of 40℃. A little computation shows that max charging voltage falls to just 14.45V at 40℃.

Daily commuters on a northern island likely won't have much problem with this temperature limit. But on this continent, we get transcontinental travelers crossing wide deserts in scorching August weather. Their batteries back in the boot, out of reach of the front seat AC, can easily exceed 40℃. And also when parked for hours in blazing sun during those heat waves.

That MK55 doesn't appear in the U.S. catalog (though I did see it in Europe). The U.S. has an M50 unit with the same specs quoted above, while other specs vary.

We also have an M40-12 SLD G-line battery, with a higher operating temperature limit of 60℃. But note that it has a lower max charging voltage of 14.6V at 25℃.

Note also this disclaimer in the technical pages:



Now let's move to those PowerSonic products. A typical spec sheet show that its maximum charging voltage is for fast charging only, and is for an even lower temperature, 20℃, and must also be temperature compensated. Just to be different than either of the two above MK products lines, this line has a maximum charging temperature of 50℃.


Continue through the technical manual to page 16, and find this:



Island commuters may not drive more than a few hours, but some transcontinental travelers here will drive all day and much of the night too, in scorching August temperatures, with nothing more than brief bladder breaks. The batteries will be hot, and charging continuously. That MK-D product line will be overheated just sitting there while charging, though the PowerSonic line will likely be fine if the charging voltage is properly reduced, and no charging system faults occur. A normally operating Prius charging system ought to be fine, but this needs to be verified, and we really should take precautions against possible faults.


Careful product selection remains important. The above discussion is consistent with the earlier paper pointing out very significant differences in thermal runaway between the makes and models tested. Fortunately, both of these product brands are claimed to meet certain certification levels, and they have reasonably detailed datasheets and technical manuals. That gives them an important leg up over the cheap mystery eBay product linked earlier.

 

You know about the change with Gen2 and Gen3 hybrid battery packs @fuzzy1 ? Toyota eliminated all the vent tubes in Gen3 packs because they decided it wasn't necessary and that the hybrid battery cooling fan was sufficient enough to evacuate any battery gasses... You know what's even more interesting... The position of the 12v battery in Gen2 Prius is right next to the external vent flap that pumps hybrid cooling exhaust out of the vehicle and there's a gap there that could easily handle 12venting.

And as someone who works on hybrid packs I put balloons over all 28 vents so I can measure the off gassing during reconditioning because venting of NiMH is real and has to be dealt with unlike your literary fantasyland of sealed 12v AGM needing venting to be safe in a car when the manufacturers have clearly seen no need for venting in all use cases of their product.

 

Who said anything about hybrid battery venting?

It is the 12V batteries that can release hydrogen sulfide. Gen3 Prii still have a vent tube attached to the 12V battery.

 

Oh, clearly you don't know anything about hydrogen sulfide hybrid battery venting history, it's evolving design, risks, etc.... Yet you present so many words and references as though you're an expert who can prove the need for venting systems for 12v batteries? Sure does undermine your credibility...

And again, zero instances of anyone on Priuschat in 20 years having a problem with no vent on their 12v battery in their Prius, yet you've dedicated more than 10 thousands words to the faux subject?

Thanks for again clarifying that your fears are unfounded and you don't have a credible leg to stand on when it comes to using a 12v mobility battery in place a standard Prius 12v battery with a useless vent tube, which costs three times as much as the mobility battery.

This is a classic example of someone worrying so much about something that will never be a problem that they're entirely blind to the primary source, of hydrogen sulfide gas inside the vehicle.

 

I found those two batteries that are made in Europe (Germany and Poland) and fit great within the battery compartment

SSB SBL 55-12i
https://wamtechnik.pl/wp-content/uploads/2020/01/SBL-55-12i-eng.pdf

NERBO NBC 55-12i
https://wamtechnik.pl/wp-content/uploads/2020/01/NBC-55-12i-eng.pdf

The issue could be a charging voltage of Toyota which is 14.7V
The manufacturer suggest charging at 14.8V maximum (at 25C)
Operating principles of lead-acid batteries - Wamtechnik

In the car, we may also have a 45C!

 

New readers arriving at this thread get the interesting job of reading some posts by somebody who does supply references that support a position, and some posts by somebody else who doesn't, but flings around a bunch of "oh, clearly you don't know anything" and "sure does undermine your credibility" at the person who does. This is helpful when you haven't got a scorecard to tell the players apart.

It's not as if we arrive here with a blank-slate, heads-or-tails, two-equally-likely-choices scenario.

We arrive here with Toyota's engineering department having already voted with their budget to put a vent hose on the 12 volt battery. Maybe that doesn't have to be the end of the conversation, but it sure is where it starts.

 

That will make @fuzzy1 feel safer knowing you're a 1/10th of a volt short of required charge power. because you know thermal runaway and all...