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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):
Hood Motor vehicle Coil Electrical wiring Engineering

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:
Hood Automotive tire Bumper Automotive fuel system Motor vehicle


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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Thanks for this great info/thread. My new to me 500e came with a dodgy looking big battery that appears to have leaked a little acid out the top and stained the plastic case at some point. It tests fine but I’m keen to swap it for one of these Mighty Max units to eliminate the risk of more leaks and corrosion and to cut weight.
ETS, where did you get those brass bits to adapt the clamps to the posts on this new battery? Ace Hardware?
 

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Thanks for this great info/thread. My new to me 500e came with a dodgy looking big battery that appears to have leaked a little acid out the top and stained the plastic case at some point. It tests fine but I’m keen to swap it for one of these Mighty Max units to eliminate the risk of more leaks and corrosion and to cut weight.
ETS, where did you get those brass bits to adapt the clamps to the posts on this new battery? Ace Hardware?
Personally I been around a lot of European cars and I’ve never seen a H series battery leak acid. H3, H4, H5, H6, H7, H8 none I’ve seen have any sort of leakage. However I have seen some Toyota’s with a H5 and H6 have some mild corrosion but no leaks. Only battery I’ve seen always leaking is the normal 35, 24, 27, 51 series etc.
 

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Discussion Starter · #53 ·
Thanks for this great info/thread... I’m keen to swap it for one of these Mighty Max units to eliminate the risk of more leaks and corrosion and to cut weight.
ETS, where did you get those brass bits to adapt the clamps to the posts on this new battery? Ace Hardware?
You're welcome. Glad to help.

It cuts COST too: My $35 6Ah is going strong at 9 months, so if it died tomorrow I'd buy another one & I still would have paid less per month than if a $110 Autozone replacement died in 2 years like the OEM sometimes does.

The brass bits were $18 from Amazon. Just search "XS Power Adapter" & scroll down until you see this:
Household hardware Cylinder Fastener Nickel Auto part


The screws shown are 6mm, but the Mighty Max is 5mm, so I got two 10-32 x 3/4" screws from the local hardware store that work fine. Ideally I'd prefer 5mm x 20mm &/or Allen heads for more torque.
 

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Personally I been around a lot of European cars and I’ve never seen a H series battery leak acid. H3, H4, H5, H6, H7, H8 none I’ve seen have any sort of leakage. However I have seen some Toyota’s with a H5 and H6 have some mild corrosion but no leaks. Only battery I’ve seen always leaking is the normal 35, 24, 27, 51 series etc.
But have you seen a battery by Xavier? This is the one in my car:

Motor vehicle Automotive tire Automotive design Automotive lighting Hood


Hood Motor vehicle Bumper Vehicle Automotive design


I rubbed at that white stain on the corner. It’s etched into the plastic. There was another post here by someone who had what appeared to be acid damage to the wiring terminals just to the right of the battery. They were told it needed a new wiring harness. I’m not taking chances. Gel battery for me, and a much smaller, cheaper one at that.
 

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Discussion Starter · #56 ·
If you always drive every couple days, you can go SUPER small.

If you ever go several days without driving, just make sure you get enough Ah for the longest you'll ever be parked unplugged with the alarm on.

I tested a 3Ah AGM & it still started the car after 4.5 days with the alarm on, & after 5.8 days with the alarm off. I'm often parked unplugged for 5 or 6 days though, so I then tested my 6Ah GEL & it still started the car after 11 days with the alarm off. I didn't test with the alarm on.

So 1.5 days per Ah is likely a relatively safe estimate IF you don't touch the car*.
Or 1.75 days per Ah with the alarm off, again if you don't touch it*.

Note that the time will be reduced with age, so just like the full-sized battery, it's wise to either carry a little jumpstarter &/or check the resting voltage periodically, preferably after parking unplugged overnight.

*If you're street-parked & get something out or put something in it cycles the strong power locks open & then closed again, even if you use the metal key. If you do that from the LEFT door it also powers up the HV drive battery contactors ("clunk" sound) AND it often also activates the brake pump ("buzzing" sound).

Unlock + open left door with contactors & pump + relock = 0.15Ah. That may not seem like a lot, but if you do that just once a day to put something in/out it reduces parking time to only about:
1.2 days per Ah with the alarm on
1.35 days per Ah with the alarm off
 

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I ordered the 12 Ah one, figuring the longest I’d let it sit would be about 2 weeks. It seems like a fair value at $50. And thanks to your posts about conserving the clunks, I’m on board with that routine. Excellent information. I can’t thank you enough. The Fiat Cares office should have you on payroll!
 

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Discussion Starter · #58 ·
LOL! I don't think they'd pay me very much for trying to keep cars OUT of dealerships, & to keep them going longer before buying a new car!

I forgot to mention someone else on this forum also got a 6Ah & says it works fine*, so your 12Ah will almost certainly be fine. It may be bigger than you really need, but it's still less than half the price of the cheapest full-size replacement, about 80% lighter, & looks like it will fit down between the frame rails just like my 6Ah, which I really like, since it not only lowers the CG even more than just the reduced weight does, it also keeps it down away from the heat of the charger & inverter.

*Mentioned on a somewhat unrelated thread, I think. I'll try to remember to find the link to post here.
 

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Good point! Fiat cares about their bottom line! And less about owners of their red headed stepchild compliance car. 😁
 

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Discussion Starter · #60 ·
Based on sales/waitlists/preorders of Tesla 3 & X, F-150e, etc, Fiat might be wise to import the 2021 500e to America, & support the original, to prove they mean business.

Over here (click here) @flat500 wrote: "I couldn't find the mighty max on their site, so I went with a Chrome Pro YTX7L-BS for $30, works perfect. It's a bit bigger than yours." HOWEVER, it's actually the exact same 6Ah as mine that has been going strong for 9 months now, parking unplugged 4-6 days every week.
 
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