Your EV's 12V Battery Can Leave You Stranded

Wait...you did know your EV still has a 12V "starter" battery, right?  Yeah, it does...whether you can see it under the hood like on a standard VICE (vehicle with internal combustion engine), it's buried under the rear cargo area (Chevy Volt, see picture below), or it's somewhere else entirely (Tesla), your car has one.  One minor exception:  The Tesla Cybertruck has a 48V auxiliary system, so none of this will apply to that vehicle. 

Prefer a video version of this?  See this Zero E-Michigan YouTube episode.  

If There's No Engine to Crank, What Does It Do?

The 12V battery may not turn over an internal combustion engine when starting the car, but it's essential to fire up all the auxiliary systems like climate control, lights, wipers, and - most importantly - the vehicle's computer that controls everything. If your 12V battery is flat, your car won't start even if the main traction battery has a 100% charge.

DC to DC Converter - Your EVs "Alternator"

During normal operation, your EV's 12V battery gets recharged not from a belt-driven alternator but from the high-voltage (400-1000V) traction battery via a DC to DC converter.  These don't typically fail as readily as, say, an alternator or serpentine belt on a VICE since they are typically solid state (i.e. no moving parts).  

Lead Acid Batteries Don't Last As Long As Lithium Ion Batteries

Just like on your old VICE, checking the battery condition is one of those maintenance items we like to put off.  But wait too long and it can leave both a VICE and an EV stranded.  When cranking the ICE, we can often hear that the starter is struggling when the 12V battery is weak.  We don't get that same feedback on an EV.  Just like your old VICE, expect to replace your EV's 12V battery about once every 2-3 years depending on its duty.  Extreme service like hot or cold weather, driving habits, or heavy auxiliary loads may reduce that life cycle.  

What Should You Do?

Car acting weird? 
Check the 12V battery.

Poor 12V battery health manifests itself in low voltage when not being charged.  Some vehicles (notably Teslas) will give drivers a warning that their vehicle's 12V battery is weak and should be replaced.  If you get that warning, don't wait too long to get it taken care of.

Other vehicles without a low-voltage sensing circuit may starts acting strange with multiple sensors giving odd readings and failures.  It's a common enough problem there even a meme for that.  In the worst case, the car is a "brick" and you get no dash lights or electrical signs of any kind.  

Check the condition of your 12V battery before the cold weather hits.  Any decent auto parts shop should be able to run a check for you.  Most will do it for free in hopes of selling you a new battery.  

12V tester on Amazon
(affiliate link)

Also check out this 12V Bluetooth battery tester on Amazon:  https://amzn.to/48QpSFz

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If you're a do-it-yourself (DIY) person, find your vehicle's 12V battery (YouTube "university" is a great resource for this) and put a voltage meter on the terminals when the car is not running and not switched to any auxiliary mode.  With no load or minimal load, a fully charged (nominal) 12V automotive battery should have a minimum fully charge voltage of about 12.6-12.7 Volts.  If it's been sitting for a few days with the telematics running (i.e. the system that communicates your car's status with online services like your smartphone app), it might be slightly lower.  If it's 11.7 Volts or below, it may be time to start shopping for a new 12V battery.  

The Chevy Volt's 12V battery 
is under the rear hatch.

There are lots of online resources to tell you more about how to check whether your battery is bad like this one from Batterystuff.com

If it's marginal, get it replaced.  This process is no different than changing the 12V battery on your VICE except perhaps the location.  Again, YouTube will come in handy if you're a DIY person.  Make sure you get exactly the same battery style and group designation paying attention to letters like "R" meaning where the positive and negative terminals are located.  There will be a "core" deposit when buying a new battery before taking your old one back.  You'll get that back when you return your worn out battery.  

Your future I-shouldn't-have-put-this-off self will thank you.  

Can You "Jump Start" an EV?

If your car does seem to have lost power to all systems, you can get a "jump start" to give the 12V system enough power to wake up the computer and run the car's systems.  Jumper cables or a jumper battery pack is still a wise thing to have with you.  Don't forget to periodically check and recharge your jumper pack or it won't help when you need it most.  

Use a jumper pack to start an ICE.

What About Jump Starting a VICE From Your EV?

Can you help a poor VICE motorist start their engine in a pinch?  That does sounds like a fun educational moment.  However, it's not a good idea. 

An EV12V battery is not typically designed for the high-current draw of a cold starting big block engine.  You can of course trickle charge their 12V battery from your 12V battery, but you might want to disconnect before they try their starter.  

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