Hybrid and EV 12 Volt Systems
Low-voltage batteries and safety on electrified vehicles.
Do hybrids and EVs still have a 12 volt battery?
Short answer: Most do; the 12 volt battery powers the computers, lights and the contactors that connect the high-voltage battery, so a weak 12 volt battery can stop a hybrid or EV from starting.
Hybrids and electric vehicles use a high-voltage battery for propulsion, but most still use a conventional 12 volt system for controls, lighting, infotainment and safety systems. The high-voltage battery charges the 12 volt battery through a DC-to-DC converter instead of an alternator.
If the 12 volt battery is weak, the vehicle may not power up, because modules cannot wake up and the contactors cannot close to connect the high-voltage battery. That makes the 12 volt battery a common cause of no-ready complaints.
Testing works much like a conventional car, but follow the maker's procedures for battery location, jump points and disconnect steps. Never touch orange high-voltage cables or components, and do not jump-start from a hybrid unless the maker allows it. Only trained technicians with proper gloves and tools should work on high-voltage systems.
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Why does a 12 volt battery fail in an EV and stop it from powering up?
Short answer: The EV's 12 volt battery powers the modules and contactors that connect the high-voltage pack; if it is weak, the vehicle cannot wake up, and it can discharge from long parking, software or module issues.
An EV still has a 12 volt system for lights, infotainment, door locks and the control modules. Before the high-voltage battery connects, those modules must wake up and close the main contactors, which needs 12 volts. A weak 12 volt battery can stop the whole vehicle from powering up.
The 12 volt battery is charged by a DC to DC converter from the high-voltage pack, mainly when the vehicle is on or charging. Long parking, frequent short use, connected app activity, or a module that will not sleep can drain it. Some EVs use a lithium 12 volt battery that needs specific testing and charging methods.
Test the 12 volt battery with a tester that supports its type, check for parasitic draw, and look for software updates. Never touch orange high-voltage cables, and follow the maker's procedure for disconnecting the 12 volt battery.
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Can I use a regular battery tester on a hybrid or EV 12 volt battery?
Short answer: Usually, if the tester supports the battery type in the vehicle; many hybrid and EV 12 volt batteries are AGM, but some are lithium, and testers built for lead-acid can give wrong results on them.
Many hybrids and EVs use an AGM 12 volt battery, and a conductance tester with an AGM setting can test it the same way as in a gas vehicle. Enter the rating printed on the battery and test with the vehicle fully asleep.
Some newer EVs use lithium-ion 12 volt batteries. Lead-acid test algorithms do not apply to them, and some makers say to check them only with their own scan tool routines. Read the label and service information before testing.
Also check the DC to DC converter output with the vehicle on, because a weak converter can look like a bad battery. Test only at the 12 volt battery or designated jump points. Never connect a tester to high-voltage components, and follow the maker's safety precautions around orange cables.
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Does a hybrid or EV need a special charger for its 12 volt battery?
Short answer: It needs a charger setting that matches the battery chemistry: an AGM setting for AGM batteries, and only a charger or method the maker approves for lithium 12 volt batteries.
The 12 volt battery in a hybrid or EV is often smaller than in a gas vehicle because it does not crank an engine. Many are AGM, which charge best with an AGM profile that limits voltage correctly. A charger set for flooded batteries can overcharge or undercharge them.
Lithium 12 volt batteries have built-in management systems, and some makers want them charged only through the vehicle or with approved equipment. Check service information before connecting any charger.
Charge at the designated terminals or jump points, especially when the battery sits in the trunk or under a seat. Use modest charge rates and a smart charger rather than high boost settings, which can stress electronics. Charge in a ventilated area, connect clamps before plugging in, and never connect a charger to high-voltage components.
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What is a portable Level 2 EV charger used for in a shop?
Short answer: A portable Level 2 charger lets a shop charge customer EVs from a suitable 240 volt outlet, for example after service, but it needs a properly rated circuit installed to code.
EVs often arrive at shops with a low state of charge, and some service procedures or road tests need more charge than the customer left. A Level 1 charger on a standard outlet charges slowly. A portable Level 2 charger connects to a 240 volt outlet and charges much faster, without a permanently mounted station.
The outlet and circuit must be rated for the charger's current, installed by a qualified electrician to local code, and protected as required. Check the charger's plug type and current settings against your outlet.
Inspect cables and plugs before each use, keep cords out of traffic paths, and never use extension cords unless the charger maker allows them. Never use a damaged cable. Check the vehicle maker's guidance for charging during service procedures, and keep the area dry.
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General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.