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if the 12V battery voltage drop. BPCM will wake-ups HV battery during the sleep cycle to charge 12V. during normal run cycle 12V battery is a buffer for the pulsing (PWM) 12V PIM charger. without good buffer there is high risk of damage to sensitive electronic components, such as EVCU OBCM BPCM CTM ORC and so on ...
 

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Discussion Starter · #22 · (Edited)
Okay, so don't run it without a 12V battery connected (I hadn't planned to).

If it goes below 11V during extended parking, you say the HV would keep it charged. 11V should be enough to start, so I might not need to bother with its switch, even for extended parking...(continued below)

check the initial charging current for the small (probably AGM battery or similar)
It is AGM, & I repeatedly felt it thoroughly, but it stayed quite cool when charging from as low as 11.38V. I'll be monitoring the charge temperature closely in order to see whether I still need to bother opening the hood while charging, as is my habit with the OEM right next to the hot electronics box.
 

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Discussion Starter · #25 ·
1) 24 days now with the tiny $20 12V still working fine, & it's still always cold, even when it's charging.

2) $20 experiment conclusion: Success. Results indicate that a $117, 1.3-pound AntiGravity ATZ7 will work.


I plan to get one & report back about that, so you can stop reading now.



#2 above is all that the experiment was originally meant for. I characteristically pushed the limit even further, proving that the $20, 3Lb MightyMax will also work long-term, at least if you disconnect it when parked unplugged, but that's a bit inconvenient. Even I can justify paying zero dollars more than the good OEM replacement that I already needed, to save 40 pounds & probably save money long-term due to Li-ion's better cycle life. When the ATZ7 discharges to only about 50% or 12.4V it shuts itself off, becoming its own jumpstarter. So there's no risk of deep discharge, or of the HV batt trying to charge it, or of needing a separate jumpstarter. Hopefully I will be able to go long enough without driving, to test how long it can park unplugged without needing to pop the hood & hit its restart button.



#1 Above: I feel it thoroughly for heat every time I start to charge it (starting the car or starting to charge the car), & a few minutes later. I feel it every time I stop charging. I usually also feel it once or twice in the middle of charging, & even in the middle of driving, if I stop to charge or shop.

HOWEVER, I haven't yet forgotten to disconnect it with its new switch when I'm going to be parked all night & day & the following night. I probably remember due to the warning above from peterwolf about extreme heat if it ever dropped to 11v while parked, & the HV kicked in & tried to force 170A into it.
 

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This fall I replaced my 12v Flooded Lead Acid, with the takeout from my motorcycle, an aftermarket LiFePO4 battery (forget the make/model at the moment) It's EXTREMELY light, and was getting a bit weak for the motorcycle (I could tell the voltage was dropping after a few seconds cranking in the cold) so I figured I'd try it.

I've run it for a bit over a month now, no issues at all, even with leaving the car for 4+days unplugged.
 

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Discussion Starter · #27 · (Edited)
Great! Thanks for reporting!

What motorbike? (so I can look up the recommended LiFePO4 replacement size)

Wait a sec! It should last 4+ MONTHS unplugged, based on peterwolf above saying that when parking drain discharges it to 11V, the drive battery kicks in to recharge it & possibly set it on fire. Is there any way for you to know whether or not it's self-charging while parked?
 

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Great! Thanks for reporting!

What motorbike? (so I can look up the recommended LiFePO4 replacement size)

Wait a sec! It should last 4+ MONTHS unplugged, based on peterwolf above saying that when parking drain discharges it to 11V, the drive battery kicks in to recharge it & possibly set it on fire. Is there any way for you to know whether or not it's self-charging while parked?

It wasn't a direct fit battery, much smaller than what was originally in the bike. (though it's an FJR1300)

no clue if the car is charging it in between, I just haven't had any issue with the battery, no 12v warnings so I'll just keep going till it gives warnings.
 

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Discussion Starter · #29 · (Edited)
Nice bike!! Its OEM batt is ~9-10Lb, ~11-12Ah. Lithium replacement is ~3Lb, ~8Ah & you noted that even when it's too degraded for the bike it works fine in a 500e. That's more proof that our OEMs are way-overkill. My new one that's also working fine is only rated at 3Ah.

1) peterwolf posted above that when it finally drops to 11V while unplugged (maybe after 5 days, or maybe only 4 days after it's aged another month) the HV kicks in to charge it, possibly at such a high rate that it will catch fire since it's too small to handle the current.

2) The 12V warning sometimes doesn't appear until after the car fails to start, so I hope you have a jumpstarter. 10.00V is reportedly the warning level, at which point there may not be sufficient current available to activate our contactors, depending on variables like 12V age, temperature, chemistry (lithium, agm, gel, flooded) etc.
 

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Discussion Starter · #30 ·
Day 34 & still fine on tiny $20 12V, but I've been disconnecting it whenever I won't be driving the next day, SO...:

I realized that before I go for lithium, I should test to see how long it can really park & stay above the supposedly ill-advised 11V (when the drive batt might try to recharge it too fast), so I broke down & got a proper voltage gauge.

First test started last night in my garage, unlocked, so the alarm is off. That's how it normally is when I'm not driving for a few days. I will test later locked for public parking.

Battery Tender.jpg
 

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Went out and looked at the model number.
Stinger Scorpion SST12B-FP.
1.7 Lb
348CCA (not like that matters at all)

Way more $$ than is reasonable to just save a few pounds in an overweight car.

BUT, I had it sitting around, so I used it.
 

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Discussion Starter · #32 · (Edited)
From their website: "$189...Scorpion does not rate their batteries with an AH rating". At 1.7Lb it was probably around 4Ah when new, but less now, like maybe around 3, like my new one....:

Good cost news is the $20 3Lb, 3Ah one is testing out highly practical so far, with over 36 hours parked unplugged & still at 12.6V. That's garaged, unlocked. Currently on track to stay above 11.4V after 7 days! That's pretty low but still fine to start a 500e. 10.0v is reportedly the warning level where it may or may not start.

It will be interesting to see any difference when I test it locked with the alarm on.


Voltages that I reported earlier were measured on OBD, which requires the 12v to be holding the contacts closed, which I later realized reduces the voltage below what it would be simply resting, which is what I am now recording & reporting.
 

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Discussion Starter · #33 · (Edited)
Results so far: $20 battery is fine even parked unplugged for over ½ week (with the alarm off) & is on track to be fine for over a week. To be extra-cautious, you could get DOUBLE the longevity with 6Ah for only $29*. At 4.4Lb that’s still WAY cheaper & lighter than OEM, even counting the one-time cost of the adaptors**. You could even QUADRUPLE it to 12Ah & 10Lb for only $40.

Starting in a couple days I should be able to test it parked unplugged with the alarm armed for a few days, & extrapolate a week from that.



Details: At 3 days + 14 hours with the alarm off, I happened to be watching as it dropped to 12.1V (about 50%)

  • Voltage drop has been very linear, so based on that, if you only drive once per week it should stay above 11.7v, which is about 25%.
  • Discharging these Absorbent Glass Mat batteries even to 20% lasts at least 100 cycles, according to BatteryUniversity.com That’s 100 weeks, nearly 2 years, or about $1/month.


* Mighty Max Battery: Motorcycle

** https://www.amazon.com/XS-Power-580...X0VZ582AARJ&psc=1&refRID=AW72FEFSRX0VZ582AARJ
 

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Discussion Starter · #34 · (Edited)
$20 3Lb BATTERY 2nd, HARSHER TEST SUCCESS!

Parked unplugged with the alarm on nearly 3 full non-stop days testing so far, & as expected for lead-acid, the very slow voltage drop is VERY steady, putting it on track to park 11.5 days & still start fine!

It also should last about 2 years, being on track to go 5 days before it hits 20% (11.6v). AGMs like this are supposed to be able to cycle that deep 100-120 times. So even if you only drive weekends & let it deplete 5 straight days a week, 52 weeks a year, 2 years is 104 cycles.

HOWEVER, it's also on track for 7.5 days to hit 11.0v, at which time the drive battery reportedly starts recharging it, possibly with too much current. I'll try to take it that low to check, but even IF it's the case, one could simply get the $29 4.4Lb double-capacity battery, for 15 days parked unplugged & probably 4 years lifespan.
 

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Discussion Starter · #36 · (Edited)
That seems like a VERY safe plan, with 4 times the capacity of mine, for about a month parked unplugged with the alarm on (when new - as it ages that will drop).

Also should be cheaper long-term, with over twice the lifespan. If mine doesn't live as long as projected, I might go for one that's 2 or 3 times its size.

Mine has now actually tested fine for a weekday-driver parked unplugged with the alarm on from 6pm Fri til 8am Tues (long weekend) with 11.9v left.

EDIT: The real limit with THIS small a 12V is 4 1/2 days parked unplugged with the alarm on, & 5 3/4 days with the alarm off.

It likely really would have stayed above 11.0v for 7 days, but even though it reportedly starts with only 10v in the OEM, THIS small battery requires 11.7v to start the car. The rest of my original post stands...



HOWEVER...:

Parked several days & opening the driver's door frequently to load/unload stuff depletes the tiny $20 12V a bit. The hatch or passenger door are fine, or with the driver's door closed ONLY 1 click. It still locks, but only with the metal key, so no alarm...

Fully opening/closing the driver's door connects the 12V to the contactors ("clunk" sound), & usually also the brake pump*. I accidentally activated my pump once on this test & it lowered the tiny battery's projected max parking time from 11.7 days to 11.5

* It seems to stay off if it had just stopped running right before shutdown.

Test result approximations, to estimate parking time for any battery size or type, including Li-ion 12V replacement:
  • 0.016A drain when parked unplugged without alarm (avg of 93 hrs).
  • 0.02A drain when parked unplugged with alarm on (avg of 103 hrs).
  • 0.12Ah total drain for each activation of contactors AND brake pump (open/close driver's door).
 

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Discussion Starter · #37 · (Edited)
Please see the important update added in red above.

Testing of the 3Lb 3Ah $20 battery seems complete, now that I took it all the way until it wouldn't start the car!
THIS tiny battery will start it at 11.7v (27%) but not at 11.6v (20%).
Slightly larger sizes MIGHT work at lower voltages, but to be safe, I'll assume they can't:

Lead-acid 12V* parked unplugged:

3Ah can go 4 1/2 days with the alarm on, or 5 3/4 with it off. (3Lb $20)
6Ah would go 9 days with the alarm, or 11 1/2 without. (4.4Lb $29)
10Ah would go 15 days with alarm, or 15 without (8Lb $30)
12Ah would go 18 days with alarm, 23 without (10Lb $40)

*A Li-ion 12V replacement should go much longer.
They have a much flatter discharge curve:
LiFePO4-vs-Lead-Acid-Discharge-Curve.png
 

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My main point right now is that for daily driving it could be fine left connected*, since parked, key off, unplugged:
  • 3Lb, 3Ah lasts 1.5+ days. DAILY DRIVERS CAN SKIP TO "MOUNTING TIPS" BELOW
  • 4Ah for 2+ days.
  • 6Ah for long weekend 8pm Fri to 8pm Mon or more.
  • 14Ah for a week or more.
*I'll likely leave my batt switch on sometime accidentally, & that could give another data point of longer time parked.

My research led me to an estimated minimum of 30mA drain while parked. If true, the above times leave about 64% remaining, so you might theoretically double them, HOWEVER...:

Nobody wants a dead battery OR to have to pop the hood to switch it off, so IF you pushed the limit like that or even further, lithium-ion has much better deep-cycle life:

- For about the cost of a Walmart OEM replacement, you can get a 1.5-pound Antigravity 3.3Ah* (so-called 7Ah Lead-acid equivalent). That should last at least a couple days connected, parked, key off, unplugged, & it has a built-in jumpstarter just in case it doesn't.
* 150 cranking amps for GayeLee & other gas cars.

- IF you already have a $40+ jumpstarter, Amazon has Li-ion 12-volt batteries starting at $65 but beware of unrealistically high "Pb-acid equivalent" Ah specs: Weight might be a better gauge, & until further testing, we can't expect them to last much more than a little over one day per pound.

MOUNTING TIPS:
  • START the threads of the terminal screws/nuts BEFORE putting the battery in place, because after that the little nuts are hard to get started, even with a little flat-head screwdriver to hold them while turning the screw. Some models avoid that with solid, threaded terminals.
  • The switch shown in post #1 requires drilling out its stock threads, to "reverse" it for control-knob clearance.

Mount Pics: OEM, removed, new, installed:

View attachment 109217 View attachment 109218 View attachment 109219 View attachment 109221 View attachment 109220
I found a 16ah on amazon for $50 it ways 4lbs. I probably should test this myself but when you turn the key on I assume that if the 12v battery is dead the propulsion battery checks for 12v power first and then fails vs just trying to charge the 12v battery?

I like the update by the way, thanks.
 

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I found a 16ah on amazon for $50 it ways 4lbs. I probably should test this myself but when you turn the key on I assume that if the 12v battery is dead the propulsion battery checks for 12v power first and then fails vs just trying to charge the 12v battery?

I like the update by the way, thanks.
Without power, how does the system "check" anything?

Yes the computer monitors incoming voltage, and has a lower cutoff voltage (around 11vdc if my reading is correct). Most ECU's in cars will not operate under 10.5v anyways, and the electrical system that controls our cars is designed off of, and uses many of the same components as, normal combustion vehicles.

The system "charges" the brakes and closes the contactors when you open the drivers door, so it can be ready to "start" when you want it to. The amperage draw from charging the brakes and closing the contactors could easily drop the voltage of the system at the ecu below 11vdc if the battery is weak, or low. If the contactors don't close, the 360vdc to 12vdc "charger" will not have any power with which to charge the 12v battery.

I'm sure if they programmed it so the brake pump only ran after the contactor closed, then we'd have less issues with a weak 12v battery, but only until something went wrong, and you didn't have assisted brakes when driving, and the 12v battery wasn't enough to recharge the brake assist. (CYA by FCA)
 

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Discussion Starter · #40 · (Edited)
Right. If my tiny 12V is too "dead" to start the car it can't power the contactors required to charge itself from the drive battery. This seemingly prevents damage from high-current self-charge by the drive battery if voltage drops too low while parked unplugged, but it could still be an issue if you park so long that it needs a jumpstart.

My 11.6v test was with my brake pump on. It doesn't always come on when opening the driver's door, or at startup. So it might be possible to "reprogram" it temporarily (for one parking cycle) by pumping the brakes until it activates right before shutting down*. Keeping it off would allow parking longer until the voltage dropped lower, since it would avoid the big voltage drop from the pump: I saw something around 5v on my gauge at one point! I wonder about leaving the driver's door closed & turning the key from the passenger seat. EDIT/UPDATE: Please see the following post.

OHHHHH! Now I wonder if that's the reason our cars sometimes start even after the 12V warning shows, & sometimes WON'T start even when it HASN'T shown yet: Maybe the warning voltage is in between what's required to start it with or without the brake pump happening to be on or off.

Since it doesn't always happen, I don't think it's a safety issue, & it almost certainly has to comply with the same gas-car safety requirement of providing 3 full brake applications even from the lowest working reservoir pressure, even after complete power failure, so I can't see any reason for the pump to come on with one key click, let alone the door. Without turning the key two clicks it won't even come out of park in order to move & require brakes.

*I will try to see how hard it is to add that habit to my twice-a-week driving schedule.
 
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