Car Battery Drain

The cluster focuses on concerns about 12V car batteries draining when vehicles are parked or off for long periods, including parasitic power draws, EV-specific behaviors, and hacky solutions like battery disconnect switches.

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#3615
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Keywords

CO HN BMW SQ5 FWIW AC youtube.com LIN FTA d.net battery car cars parked voltage disconnect trunk electric parking power

Sample Comments

vonseel Jan 21, 2019 View on HN

How does this not kill your car battery?

CrendKing Oct 22, 2023 View on HN

Maybe you could disconnect the battery cable every time you stop, and reconnect before you go?

teamonkey Feb 24, 2012 View on HN

Consider a battery failure while parked on a hill

JulianMorrison Feb 22, 2012 View on HN

Why can't the battery just be simply disconnected?

TheSoftwareGuy Jun 11, 2025 View on HN

I'd be wary of draining the battery while the car is off. You don't want to prevent the car from starting

BLKNSLVR Oct 3, 2022 View on HN

They're not using the car, so the battery isn't depleting.

K2h Nov 30, 2012 View on HN

I wonder what the power draw is? a tad worried my car wont start after longterm parking.

JohnFen Apr 10, 2023 View on HN

I wonder if installing a switch to disconnect the car's battery entirely would be an acceptable (but obviously hacky) solution.

goodcanadian Aug 12, 2019 View on HN

I can only speak for the Leaf, but much like a petrol/gasoline car, the 12V battery is only charged when the car is on (and when the car is actively being charged). It is entirely possible to run down the 12V battery if you leave the car parked long enough without it being turned on. Once the 12V runs down far enough, you are no longer able to turn the car on (or charge it) as the 12V powers the contactors for the main battery. I have had to jump start my Leaf due to a bad 12V battery.

toomanybeersies Apr 19, 2016 View on HN

What if the thieves remove the battery because they're parting out the car?