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Discussion Starter · #1 · (Edited)
My 2015 500e is dead in the driveway - again. This has happened before when the car has sat for weeks unused, so it's not entirely unexpected, but I'm beginning to wonder if I'm damaging the car by letting it sit unused on an L1 charger 24/7. I've replaced the 12v battery twice over the past two years, and will get it jumped and replace the battery every so often if need be, but I don't want to be damaging the car while it's just sitting in the driveway.

Am I damaging the car by letting it sit unused, plugged in, for weeks or months at a time?
 

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No damage. According to the manual you should leave it plugged in & that will top off the 12V battery every 3 weeks.

However the car will not awaken to do that if your 12V dies in under 3 weeks due to being worn out.

I didn't say "due to being old", because even a young 12V can die in a 500e. Someone complained about theirs dying "every 6 months". A more believable report was 23 months.

This seems to be due to heat from the adjacent onboard charger which gets pretty warm even on L1, & radiates that heat constantly to the 12V for about five times as long as the car is driven.

That's why I recommend charging at cooler times/places & leaving the hood open when practical. I also added a piece of styrofoam insulation, & deleted the heat-trapping motor cover. Mine was still good after 5 years (but I replaced it then anyway):
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Before:
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After:
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Discussion Starter · #3 ·
Got it. Turns out when I check the records, the battery was last replaced 23 months ago and 14 months before that, so it's probably time.

I'll replace the battery, remove the cover, and scrounge up some stryofoam. Thank you!!

Pamela
 

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You don't need a new battery if it starts the car after it rests without charging for as long as you ever leave it like that, for example all day at work, or all night after it's done charging at 8pm.

Nearly nobody ever sees any warning before the 12V fails to start the car. I just posted a new thread about that, but in order to avoid being stranded by a battery that's so dead that it won't even jumpstart* I very strongly recommend getting a Bluetooth battery gauge with an alarm you can set to go off whenever any driver with the app gets within about 30 feet of the car. For example this $33 BM6:
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If you get one of those first, then you can see how long it goes before dropping near 11.6V, & THEN decide whether or not to replace the 12V or just get a trickle charger.

* It's possible that even then it might start if you use old-fashioned cables & disconnect the dead battery until the car is in "ready" mode, but it might not keep running once the dead battery is reconnected, & it might damage delicate electronics if you run it with no battery.
 

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Keep in mind that even a brand new $120 Interstate battery will only last about 11 weeks parked.

Your 500e killed one battery in 14 months, so it may be half-dead in 7 months, lasting only 5.5 weeks parked.

So depending on how many weeks you need it to sit, you might need a trickle charger soon anyway.

I hope that made sense.
 

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This one got 4.8 stars out of 40,502 Amazon reviews:

 

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Discussion Starter · #8 ·
Keep in mind that even a brand new $120 Interstate battery will only last about 11 weeks parked.

Your 500e killed one battery in 14 months, so it may be half-dead in 7 months, lasting only 5.5 weeks parked.

So depending on how many weeks you need it to sit, you might need a trickle charger soon anyway.

I hope that made sense.
No doubt that makes good sense. I don't have much of an understanding of how battery life works, but I'll take your word for it and get a wi-fi sensor. Even though the car is parked in my driveway, it's on a public alley and I don't want to invite inquisitive passersby to steal the trickle charger. (Alas, the car is an eye-catcher.)
 

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Discussion Starter · #9 ·
Your battery may not need replacement. A trickle charger might be a better investment.
Running a trickle charger in my driveway isn't an option because it would invite theft and we've had problems with that.

So, I did have the battery replaced between reading your initial reply and seeing the subsequent notes about the trickle charger and the wi-fi monitor. I had bought it 23 months ago from AAA (American Automobile Association), so technically it was still under warranty. I had them come out on a roadside assistance call. They tested the battery and said that it only needed recharging and they weren't convinced it wouldn't hold a charge, so they declined to replace it under warranty. They were skeptical of my claim (based on what I had read here) that the Fiat was charging the 12v battery while plugged in, but they tested it and you were (no surprise) correct: it was charging the 12v battery when I plugged it in, and not when I unplugged it. Still, they would not replace it under warranty and I wasn't going to cause an argument in my driveway.

So the battery replacement was at my expense. I'll install a wi-fi battery monitor, and make sure to drive the car more regularly.

What I don't quite understand is why the car itself - if it's charging the 12v while it's plugged in - isn't the functional equivalent of a trickle charger?
 

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Discussion Starter · #10 ·
For what it's worth, here is the battery test report on the old battery:
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and the new battery:

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I'd be curious about your opinion as to whether they should have replace it under warranty, if you have one...

Thanks again for all your help,
Pamela
 

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Unless you charge the old battery & then use the monitor you're getting to make sure it holds a charge, you can't tell if it was fine or not, so without doing that first it's unreasonable to expect a warranty.

You can just run a cheap thin extension cord into the hood, with the hood closed on it, locking the trickle-charger in the motor compartment. Ideally run the cord around the left mirror as a reminder so you don't drive off dragging the cord.

I suggested a Bluetooth monitor. WiFi is only good if you'll always be near a reliable signal when it's been resting a while. For example it wouldn't work if your kids take it & have to park down the street from a friend's house when they're gone all day in the friend's car.

The 500e provides full charging current to the 12V any time the key is on, 1 click or 2, so there's no need to drive the car to charge the 12V. Just turn it on for a while.

  • A trickle charger runs constantly, keeping the 12V topped off whenever it needs it.
  • When the car is plugged in, it only charges the 12V every 3 weeks.
 

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Discussion Starter · #13 ·
Unless you charge the old battery & then use the monitor you're getting to make sure it holds a charge, you can't tell if it was fine or not, so without doing that first it's unreasonable to expect a warranty.

You can just run a cheap thin extension cord into the hood, with the hood closed on it, locking the trickle-charger in the motor compartment. Ideally run the cord around the left mirror as a reminder so you don't drive off dragging the cord.

I suggested a Bluetooth monitor. WiFi is only good if you'll always be near a reliable signal when it's been resting a while. For example it wouldn't work if your kids take it & have to park down the street from a friend's house when they're gone all day in the friend's car.

The 500e provides full charging current to the 12V any time the key is on, 1 click or 2, so there's no need to drive the car to charge the 12V. Just turn it on for a while.

  • A trickle charger runs constantly, keeping the 12V topped off whenever it needs it.
  • When the car is plugged in, it only charges the 12V every 3 weeks.
Agree about the warranty.
Also understand about wi-fi/Bluetooth - the monitor I ordered is bluetooth, not wi-fi.

And thank you for the clarification about the fact that the car only needs to be turned on, not driven. Much easier!

To re-cap: The car was last used and then fully recharged on a Saturday; by the following Thursday - six days later - it would not start while unplugged. So, the 12v battery was not holding a charge for six days, possibly fewer. If I'd had the Bluetooth monitor installed, I might have avoided replacing the 12v by waking the car up (turning it on) when the 12v was down to 30%. Do I have it right, at last?
 

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You have it right.

As for your new details of "Saturday to Thursday": In normal use, driving at least 40 miles a week, a 2-yr-old AAA battery won't die just from resting 6 days.

However it will die if you do this in a gas car or an EV:
  1. Let the car sit for several weeks until one Saturday the 12V is nearly dead & will just barely start the car (11.6V for a 500e).
  2. Drive just a few miles so the 12V only gets a tiny bit of recharging & is still nearly dead.
  3. If it's an EV, recharge the car right away so that the 12V will be sitting uncharged for as long as possible.
By Thursday it will be dead.
 

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Since this sounds like a 12V battery topic- some people on these forums have tested various lithium ion 12V battery replacements. A few models are inexpensive, about $20.

Electric Tire Shredder tested a cheap 12V li-ion battery on his post: Tiny $20 12V Battery Works! (& saves 38 Pounds). You could buy multiple of these for the cost of a new 12V lead acid replacement.

Prior to that post, back in July 2020 I replaced the OEM lead 12V in my 2016 500e with a Group 47/H5 Antigravity 12V battery which at the time was a lot cheaper than it was today and was also on sale. I'm not recommending for cost since it retails ~$660 atm. It was a direct-size replacement with a 5-year warranty, Battery Management System, and emergency jump start reserve (which I've never had to use). They were estimating 8-12 years battery life back then. I replaced the battery on July 2020, so this is 2.5 years later and of course no problems yet.
 

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IMO they should have replaced it under warranty - or at least charged it and tested it again. The only way I could see a good battery draining to that low of a voltage in 6 days is if there was an external load on the battery.

It may be worth monitoring your new 12 volt battery voltage to make sure there isn't something draining it. All you need to do this is a voltmeter. After the car has been sitting for several days check the voltage. It should still be above 12 volts.
 

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Discussion Starter · #18 ·

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make sure there isn't something draining it... After the car has been sitting for several days check the voltage. It should still be above 12 volts.
That is excellent advice. Thank you! @Seattle500e should do that with the Bluetooth volt gauge, prior to hooking up the solar tricklecharger.

The only way I could see a good battery draining to that low of a voltage in 6 days is if there was an external load on the battery.
There is another way. Post #14 above describes its 3 steps. Based on some extra details which @Seattle500e gave me in a PM, that seems to be what likely happened.

IMO they should have replaced it under warranty - or at least charged it and tested it again.
Ya, I'd call AAA to see if it's too late to have them fully charge the old battery & then test its voltage a few days later in order to give a warranty credit. However I would bet on it being okay, meaning no credit, but at least the car has a brand new battery now.
 

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I'm leaning toward it not being okay. To go from a voltage that was able to start the car drive it some distance (charging the 12 volt battery) then plugging it into charge (also charging the 12 volt battery), then go all the way down to 0 volts in 6 days means either there was a drain on the battery or the battery was bad. My guess is we will never know for sure if it was a bad battery since it was likely turned in for the core when she bought the new one.

The fact that it has happened before does increase the probability that there is some external drain when the car is off. This is something that you can check for.
 
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