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Discussion Starter · #41 · (Edited)
After parking for only 73 hours with the alarm off, it was already down to 11.65v! (gauge flashing between 11.6 & 11.7)

Since that's even less time than when I tested with the alarm on, I suspect that I may have killed the poor little thing by taking it to 5v under the load of the brake pump at startup after the 4.5 day alarm-on test. I should have done it from the passenger seat...:

This time, I figured I'd better start it from the passenger seat & that worked fine, even with the brake pump activating. I didn't have the nerve to try only one key click to see if that was okay. I just turned it quickly all the way, but it's at least worth trying, if it ever won't start from the driver's side where the pump drops the voltage as soon as you open the door.

I remembered to try the brake "reset" from above, which so far seems to prevent the door from activating the pump.
 

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Discussion Starter · #42 · (Edited)
Short Update: The tiny $20 3Lb 3Ah still seems fine for weekday commutes & even 3-day weekends left alone parked unplugged, although I recommend the GEL model. However I often park 4 days with no plug, so I ordered a $35 4.4Lb 6Ah GEL direct from MightyMaxBattery.com.

Long Version: I left my hood ajar last night, & the alarm off, to check the voltage before & after unlocking the car today. 12.6v before, & 12.5 after, even using the key so no lights flashed! It might have been at 12.55 & only dropped to 12.54, but the point is it does take a bit of a bite out. In the 73 hour test 4 days ago I had unlocked & relocked at least twice, so I still believe that for daily weekday driving the 3Ah is fine, & even okay for a long weekend IF you don't unlock & relock it! I'm also not 100% certain that I had turned off my OBD dongle (I often forget to), however...:
  • Nearly every week I'm parked for 3-5 days with no plug access at all,
  • Sometimes I need to unlock/relock to load/unload things,
  • Sometimes I forget to turn off my OBD dongle,
  • I don't want to wear out my contactors, turning the key one click for a few minutes to recharge the 12V,
  • Doubling it to 6Ah is still very light & cheap.
Compared to AGM lead-acid batteries, GEL is supposedly more tolerant of:
  • heat from our onboard Li-ion charger,
  • slight overvoltage from our 12V charger,
  • deeper discharge from parking unplugged for several days.
Gel's primary drawback is higher cost, but with such a small size there's little difference. I would have got the 3Ah in gel but it didn't show on Amazon at the time.

Amazon again didn't show all models of their top-rated Mighty Max, but MightyMaxBattery.com did, for the same price, free shipping, & less tax. Tip: If you put one in your cart & wait a while after entering your email, you might get a 5% coupon! (like I got AFTER quickly placing my order).
 

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Discussion Starter · #43 · (Edited)
I learned/realized a few more things from a final 6-day parked-unplugged test of the now-abused* 3Ah battery:

- For ANY size 12v battery, a fix for its faulty warning** would be an inside mount of the add-on volt gauge shown in post #30 above. Way before it's too low to start from the right side, it flashes red non-stop, without even touching it. It starts flashing at 11.6V (20%) which is a 10% safety buffer:

- The tiny 3Ah was on track to go nearly 7 full days & still start: It started with only 11.3v (10%!) with the left door closed to avoid pre-activating the contactors & brake pump. It wouldn't start from only 11.2v though (7%).

- If yours fails to start, wait 15 minutes with it off & try again from the right because that long after my failed start it went back up 0.7v.

- Having completed all the software updates, my drive battery never self-connected to charge the starter battery. I tested all the way down to 4.0V, so there's no worry about it catching fire if left parked too long unplugged. If you DID let it get so low it needed a jump, it would still be wise to check it for heat after starting, although it has always been stone-cold when charging, even from 20% (11.6v).

* I drained it all the way down to 0% once, & then all the way to 20%, before this test.
** No warning showed before or after failing to start at 11.2v
 

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Discussion Starter · #44 ·
The 6Ah is still working perfectly after a few months. As indicated above, I got tired of switching it off every time that I was at my friend's with no plug & didn't know if I'd be staying 4 days or 5 without driving.

I replaced the $20 3Lb 3Ah AGM with this $35 4.4Lb 6Ah GEL (YTZ7S - click to enlarge):
20210114_153843.jpg
It's the biggest I saw that still fits nice & low between the irremovable rails, well away from charger heat, although GEL is supposed to be more heat resistant. I tested, & it still starts the car after parking unplugged over 11 days with the alarm off in my mild coastal southern CA underground garage.

12.2V after 6.5 days unplugged with the alarm off:
20210114_154017.jpg

For colder climates where freezing weather reduces voltage, depending on how cold it got, & how long I wanted to park unplugged without having to bother with a cutoff switch, I might go for a $55 10Lb 12Ah or even a $60 12Lb 18Ah, since even the latter is still much cheaper & lighter than an OEM replacement.
 

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The 6Ah is still working perfectly after a few months. As indicated above, I got tired of switching it off every time that I was at my friend's with no plug & didn't know if I'd be staying 4 days or 5 without driving.

I replaced the $20 3Lb 3Ah AGM with this $35 4.4Lb 6Ah GEL (YTZ7S - click to enlarge):
View attachment 109644
It's the biggest I saw that still fits nice & low between the irremovable rails, well away from charger heat, although GEL is supposed to be more heat resistant. I tested, & it still starts the car after parking unplugged over 11 days with the alarm off in my mild coastal southern CA underground garage.

12.2V after 6.5 days unplugged with the alarm off:
View attachment 109643

For colder climates where freezing weather reduces voltage, depending on how cold it got, & how long I wanted to park unplugged without having to bother with a cutoff switch, I might go for a $55 10Lb 12Ah or even a $60 12Lb 18Ah, since even the latter is still much cheaper & lighter than an OEM replacement.
Happy to see the experiment with a smaller battery - but wanted to share my experience with the Mitsubishi Outlader PHEV (hybrid). That car has a small 12V as it is only needed for the computers and electronics - the “take off” is always on the EV motor. The high voltage battery is used to charge the small 12V regularly. However when the high voltage battery is empty that no longer works and then leaving the interior light on for an hour drains the small 12V battery to the point that the computer can’t cope and no longer starts (or charges!).
So there sits a pretty sizeable car with a 2L engine and 4wheel electric gear dead on the street. Took the 12V battery from my 0.6L oldtimer to fire it up... (this happened 3x in the course of 3 years, as it also has a wifi connection which i suspect gets powered continuously as well)

So I was happy to see a fullsize 12V in the Fiat 500e - gives a little bit more wiggle room for human mistakes and for techie mistakes such as leaving the OBD module plugged in.
 

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Discussion Starter · #46 · (Edited)
Thanks for sharing, but it seems almost completely* irrelevant: Your PHEV & our BEVs should really swap 12V battery sizes. Unlike your own typical PHEV habits, our BEV battery is charging our 12V batteries the entire time that the key is on, since the drive battery is never, ever empty except RIGHT before plugging in, which also recharges the 12V the entire time the car is charging.

Even on L2, that charge time is equal or longer than the entire time it was being driven (unless you average under 25mph). On L1 it's about 5 or more times as long as the drive!

Also our interior lights all go off after 15 minutes & won't come on again without the key being on (which again charges the 12V).

*We have no wifi, BUT one valid point you bring up is that in the 3 years after initial customer pickup when the remote app access functions, it might drain more power than my 2013, while parked unplugged.


SO, my new "double-sized" 6Ah allows me plenty of wiggle room for my own human mistakes like leaving my OBD module powered up when I'm parked unplugged for over 4 days. That's why I upsized to it from the 3Ah.

I also tend to forget something in my car, like a flash-drive, &/or forget to leave the hood cracked if I feel like checking the volt meter after several days. Cycling the power locks to take care of those takes a surprising amount of power, but that's also easily handled by the 6Ah's capacity.
 

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Note that the average daily commuter using L1 goes only about a maximum of only 8 hours* between charging the 12V on workdays, since it charges while driving AND while charging.

IF the car is home all weekend, it's about a maximum of 2.3 days with the 12V uncharged.

*20 mile drive (charges the 12V), park at work 8 hours, 20 miles home, 8 hours to recharge, then max 8 hours parked off charge before driving again.
I was thinking maybe 10AH LiFePo4 should get you 10 days. I did notice that I changed an incandescent bulb to LED in the trunk area and now that bulb is on really dim all the time, maybe that is eating the battery.
 

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Discussion Starter · #48 · (Edited)
"all the time"? Even after 15 minutes unplugged/key-out when my rather pathetic OEM hatch light shuts itself off? (my PRND LEDs stay on really dim while charging)

10Ah LiFePO4 should last closer to 19 days parked unplugged with the alarm armed, EXCEPT an AntiGravity "ReStart", which would shut itself off after "only" about 13 days, but then you just use it's "ReStart" feature, & then reset your date/time display (& lose any saved trip gauge readings).

In case I come into some money before my 6Ah dies, I've been considering these LiFePO4s:

AntiGravity:

AT12BS-RS (6.1Ah, 2.3Lb $202, 11 days parked unplugged*, fits down between stock frame rails)
ATX12-AH-RS (6.6Ah, 2.6Lb $225, 12 days parked unplugged*, fits down between stock frame rails)
AT12BS-HD-RS (8Ah, 2.9Lb, $234, 14 days parked unplugged*, fits down between stock frame rails)
* but just hit "ReStart" after that.

Banshee: YTX9A (8Ah, 2.7Lb, $87, 15 days parked unplugged but no "restart", fits down between stock frame rails)
 

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Discussion Starter · #50 · (Edited)
"ReStart" (tm registered?) is AntiGravity's (patented?) system where it shuts itself off if it ever drops below 12.4v

After that, if equipped you hit the wireless key fob button. If not, you use the metal key to unlock the door, pop the hood, & hit the button on the battery.

Now I'm considering the $130 Antigravity ATZ7, since I rarely go without driving for the ~6 days it would take for it to even just need me to pop the hood & hit the button (& I can handle the latter!). At home in my garage with the alarm off it should go ~7.5 days, but there I can just plug in a $40 BatteryTender.com trickle charger.
 
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