In a recent column a reader asked about a plug-in hybrid and the status of the gas. The discussion also mentioned the possibility that the 12v “starter” battery could drain over time. I don’t know about other cars but the Kia Niro has an “override” that can use the EV battery to start the car. That was the situation when we originally bought our Niro. There is a button on the dash that, if the 12v battery will not start the car, enables the starter to pull the necessary power to start the car. The battery then charges as normal. We have had no starting problems since that initial situation where the car had sat for several months before we bought it.
All Toyota hybrids and PHEVs (and many others, like my MKZ hybrid) use the large hybrid battery and one of the hybrid motors to start the car. The problem with a dead 12V battery is that it is used to power all the accessories and much of electronics, so a dead 12V = no start.
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All batteries drain over time. Lead acid more than Li-Ion. And all cars never completely turn off and drain a very small amount when the car is off.
That said, the Niro’s system design is smart. There is no reason a hybrid or plug in hybrid should not be able to do this.
My Chevy Volt (plugin hybrid) does the same. Hybrids do not have a traditional starter motor. The electric motor(s) turn the gas engine to start it. Very quickly and quietly I might add. When my car decides to start the engine I hardly know it’s running!
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Looks like the Niro uses a ‘hybrid starter generator (HSG)’ driven by the serpentine belt. Interesting to have the starting dependent on a belt. But it uses the hybrid battery, not the 12V battery, for power, as far as I can tell, just like other hybrids.
There are as many different starter configurations as there are PHEV designs. Some use a conventional 12V battery and starter, some use an aux 12V battery, some use the high voltage battery and motor to start the engine, some use both depending on what’s happening with the car.
It’s useful to remember that any HV component is managed by a 12V control system, so if the main 12V battery is dead, so is the hybrid system.
Conversely, on some cars, if the hybrid system is inoperative due to a fault or simply design limits (like outside temp too cold), the gas engine is inop as well.
I imagine there are, but I’m only familiar with the ones that use the high voltage systems. Which ones use the 12V system?
Mercedes has some ‘mild hybrids’ with a 48V battery, I’d guess that’s the only battery.
Not all Toyota’s, the 2024/2025 Tacoma Hybrids are not PHEV’s and you can still get at least the Corolla Hybrid and the Prius in non PHEV… I think that most of the Toyota Hybrids are not PHEV’s…