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Re: 12V battery BCI Size?

Posted: Thu Feb 28, 2019 4:14 pm
by Lithim
This must be the month for 2012 model year batteries to die. (Obtained my 2012 in February, 2013
Mine cratered over the last week. 10.6 volts (still could get ready light to come on) to now 8.4 volts and nothing happens.
Can I put a battery charger on it to get the voltage high enough to start the car? The manual indicates that cables must be disconnected to charge the battery. Is that true or can it be charged safely while still connected.
Interstate seems to have the correct group size replacement.
Stay charged my friend.

Re: 12V battery BCI Size?

Posted: Fri Mar 01, 2019 3:32 am
by kiev
In your case i would not recommend that you try to charge the Aux battery and start your car, nor try to charge the pack until you get a new 12V Aux.

The damage that can result with trying to operate the car with a defective Aux power supply is very expensive.

Re: 12V battery BCI Size?

Posted: Fri Mar 01, 2019 3:37 pm
by Lithim
151R is the correct group size. Changed my lifeless original (2012) battery today for a new Interstate flooded lead acid.
Getting the positive connection disconnected was tricky since there is not much slack in that cable.
All is good.
Stay charged my friend.

Re: 12V battery BCI Size?

Posted: Tue Mar 12, 2019 2:53 pm
by Don
I *finally* got around to replacing the battery in our second car today. The OEM one was 7+ years old and had never shown any signs of getting weak, but I prefer to change things before they cause me problems. Used a Miata AGM again like I did in the first car 3 or 4 years ago. Ordered from Battery Mart for $107.95 with free shipping. Comes fully charged, sealed, maintenance-free and with a one year warranty

To it's credit, the OEM 151R served very well, considering I never added water to it . . . . and it was still working fine when I removed it

So now after 7+ years, both cars have required the same amount of 'maintenance.' One set of tires for each, one set of wiper blades for each, one battery . . . . and, that's about it. First really nice day, I think I'll drain and refill the transmissions. Really can't think of much else to pamper them with. Amazing cars, especially when you consider many hundreds of 3, 5, 7 or 10 mile trips are just about the worst kind of service you can subject any automobile to. We have other cars which rely on trickle chargers to be ready to go because they are so seldom driven. State Farm is making a mint off us insuring cars which seldom leave the garage


Re: 12V battery BCI Size?

Posted: Thu Mar 14, 2019 4:06 pm
by sheinr4143
Big shout out :D to members of this forum for emphasizing the need to monitor the health of aging auxiliary batteries. Used a conductance tester to determine that our factory installed (December 2011) Yuasa battery was degraded by use, time, and temperature fluctuation. The vehicle never exhibited any symptoms of 12v battery degradation over the 7+ years of service life, and we hope to enjoy a similar trouble free and extended period of service from the replacement Bosch 151R.

Many thanks!


Re: 12V battery BCI Size?

Posted: Mon Apr 08, 2019 5:59 am
by sventchik

does anybody know if it's possible to charge the main battery, but in parallel remove the 12V battery ?

In fact, I would like to charge the 12V battery with an external charger (this charger has several modes, impulse and low currant to bring older batteries to better condition)

Thanks for advice ;)

Re: 12V battery BCI Size?

Posted: Sat Apr 13, 2019 6:43 am
by pbui19
I am so tempted to try out this LiFe 12-v aux lead replacement: ... assed.aspx

While the spec specifically says "Must use LiFePO4 charging circuit. Do not use Lead Acid charger to charge this battery"; I am wondering if it's just to cover disclosure.

My thinking is that there is a built-in BMS with single cell as well as pack monitoring. It looks like this is what inside, including info on the BMS which is called PCB: ... .5-mm.aspx

I am more concerned about keeping this 12-v LiFe pack at high SOC, due to the dc/dc charging it at 14.2v; so perhaps the LiFe can be parallel to a 12-v SLA.

What is to be gained? What is the Benefit?

Posted: Sat Apr 13, 2019 7:19 am
by kiev
But why-- Because it weighs less? That is too little useless a benefit for the risk of failure.

The price for this little UPS battery is the same as the full-sized lead acid in the miev. Plus it is way undersized for the current loads of a running car with headlights ON.

The chemistry requires a different charging procedure, so a new charrger from the 12V converter output to the LiFePO4 is needed.

Sure it has an internal BMS, but all lithium packs do (unless is was a diy). A BMS is not a charrger, it provides a cutoff mechanism to try to prevent pack damage.

Re: 12V battery BCI Size?

Posted: Sat Apr 13, 2019 6:23 pm
by WReed82
Hi PBUI19,

Can this battery be charged at below freezing temperatures?
Does it freeze where you are?

Lithium Titanate batteries can be charged below freezing, will likely be on the market before the end of the year.

Thanks and good health, Weogo

[quote="pbui19"]I am so tempted to try out this LiFe 12-v aux lead replacement:

Re: 12V battery BCI Size?

Posted: Mon Apr 15, 2019 1:33 pm
by pbui19
I happen to have a couple of those UPS 7A LiFe lying around unused, and no I would not pay the extra $ just to get them.

It just bugs me that the EV manufacturers are still using lead for the aux, and in particular Mistu because of the potential harm to the charger/inverter. In general, EVs are so "advance" with minimum maintenance and there is this consumable lead acid battery. The iMiev 12v really should last a lot longer than normal ICE usage, given the benign load and operating condition. But that's what I thought about the Prius 12v aux as well. Lead just sux. I haven't gotten my Tesla yet, but if Tesla also has lead 12v, that's just sad.

Does any one know the max current drawn from the 12v aux ? I vaguely recall Joes measured just under 10A. Ideally, by reducing the dc/dc charger voltage from 14.4v to 13.5v, (which gives 13.5/4-cell = 3.375v/cell) , these LiFe should be happy for a long time.

I am in northern CA and it rarely goes below freezing. I don't think these LiFe can handle low temperature and am doubtful if the BMS even monitor temperature.