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 Post subject: 12V Battery failure-Catastrophic Can the car cause this?
PostPosted: Fri Jul 12, 2019 5:19 am 
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Joined: Wed Jan 29, 2014 10:40 pm
Posts: 45
Location: Oakland, Ca
Hi,

I did a 200 mile drive today. While charging with JDemo, I noticed a bad smell that made me gag and choke. It turns out that my Bosch AGM 12V battery was probably overheated, venting in the way a tea kettle vents. I managed to get home with the AC on recirc, since the battery continued to vent while driving.

Once home, voltage was 13.2 on the battery, 14.25 with the car in ready. I let the battery cool and stop venting. Afterwards, the car wouldn't start. I pulled the battery and brought it to Pep Boys. The battery test revealed 13.14 volts, 1 CCA. They did replace the battery under warranty. The manager feels the reason for failure is from a problem in the car.

I installed the battery this evening. Without attaching the ground, there is 11.8V from the chassis to the negative terminal. I don't think this is normal, but don't have much experience. Could this be a short in the 12V system? Or is the vehicle charging system not designed for an AGM battery?

Of note, the traction motor and onboard charger were replaced 2 weeks ago. There are no error messages, the car drives normally. No other electric gremlins.

Thanks in advance for the help.

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 Post subject: Re: 12V Battery failure-Catastrophic Can the car cause this
PostPosted: Fri Jul 12, 2019 5:31 am 
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Joined: Thu Jan 17, 2013 11:13 pm
Posts: 1766
Location: Los Altos, CA
My Bosch battery vented too when I left the car on all weekend while camping. Don't do that. It is a known compatibility problem with AGM and automotive lead acid charging strategy. My battery has been fine for the year since it vented. Maybe I'm lucky.

The voltage from negative terminal to chassis is there because you didn't connect it yet. That is the battery voltage above the "dead" car. You can connect your meter to measure amperage and you will see the in-rush current as the battery starts to power the car, then the steady state amperage draw. That initial voltage is why you usually see a small spark when you first connect the battery.

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2012 Shoreline Blue #1462 w/JdeMO | 2018 Tesla Model 3 LR | 4.32kW Motech/Enphase PV Solar + 2x Powerwall 2 AC| Leviton EVB40 40A & Jesla Home Charging | 2015 e-Golf LE (returned)


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 Post subject: Re: 12V Battery failure-Catastrophic Can the car cause this
PostPosted: Fri Jul 12, 2019 6:50 pm 
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Joined: Tue Jun 06, 2017 3:55 pm
Posts: 11
DC converter acts as 12v charger when in key on mode. Its charge curve is setup for lead acid battery not AGM. Curves are very different for the two types of batteries. I would never put an AGM into the RAV EV for this very reason. I have seen the same problems on the nissan leaf and chevy bolt. Most every EV manufacture setups the DC converter to charge a Lead Acid battery only since they are most common and most robust and known batteries in the car space. The 12v battery is meant to be a backup for the dc converter and to handle the surge loads on the 12 v bus. Best battery for this is therefore the common robust lead acid type, which last 4-7 years in normal useage. AGMs on the other hand are highly susceptible to overcharging and popping their vent valve, releasing hydrogen gas and usually ruining the battery. The reliability of lead acid is why every car OEM uses and continues to use them for the vital 12v bus!

Steve
2012 RAV
2011 Leaf


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 Post subject: Re: 12V Battery failure-Catastrophic Can the car cause this
PostPosted: Fri Jul 12, 2019 10:58 pm 
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Joined: Mon Apr 01, 2013 11:42 pm
Posts: 295
Location: San Diego, CA, USA
miimura wrote:
My Bosch battery vented too when I left the car on all weekend while camping. Don't do that. It is a known compatibility problem with AGM and automotive lead acid charging strategy. My battery has been fine for the year since it vented. Maybe I'm lucky.
...


So your theory is that this happened because the car was "on" too long? This is pretty much unavoidable when traveling with Jdemo as you leave the car on while charging. I'm really curious as my lead-acid Interstate battery just hit 4 years old, and I was ready to replace it with the recommended Bosch.

Of course, people have been using AGM because the regular lead-acid batteries seem to suffer in electric cars from too much cycling. I'm interesting whether many other people have had problems with the AGM batteries.


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 Post subject: Re: 12V Battery failure-Catastrophic Can the car cause this
PostPosted: Sat Jul 13, 2019 6:52 am 
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Joined: Thu Jan 17, 2013 11:13 pm
Posts: 1766
Location: Los Altos, CA
davewill wrote:
miimura wrote:
My Bosch battery vented too when I left the car on all weekend while camping. Don't do that. It is a known compatibility problem with AGM and automotive lead acid charging strategy. My battery has been fine for the year since it vented. Maybe I'm lucky.
...


So your theory is that this happened because the car was "on" too long? This is pretty much unavoidable when traveling with Jdemo as you leave the car on while charging. I'm really curious as my lead-acid Interstate battery just hit 4 years old, and I was ready to replace it with the recommended Bosch.

Of course, people have been using AGM because the regular lead-acid batteries seem to suffer in electric cars from too much cycling. I'm interesting whether many other people have had problems with the AGM batteries.

Yes, if you look at Battery University, the AGM can bulk charge at the typical lead acid voltage of 14.4V, but the float voltage should be reduced to 13.8V. So, you should give the battery a break every 4 hours or so and probably even try to discharge it a little between multiple hour drives. After the AGM is fully charged at 14.4V it starts generating heat, then it vents when it overheats.

The main reason that the AGM is generally good for the RAV4 EV is that it has very good standby energy capacity to support the idle draw of the RAV4 EV when parked. If you routinely drive with multiple back to back JdeMO sessions and don't turn the car off, I would not recommend the Bosch battery.

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2012 Shoreline Blue #1462 w/JdeMO | 2018 Tesla Model 3 LR | 4.32kW Motech/Enphase PV Solar + 2x Powerwall 2 AC| Leviton EVB40 40A & Jesla Home Charging | 2015 e-Golf LE (returned)


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