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My car is around 8 years old now.

I had a cheap USB inverters to charge my phone in my Toyota for 8 years and it recently died. Then I bought another another cheap USB inverter and it worked for maybe a week and also fried.

I was planning on buying something a bit more high end, with a name brand this time... But now i'm thinking something might be wrong with my car.

Thoughts how I should handle the situation?

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  • Why do you have an inverter to charge a phone? The point of an inverter is to convert DC to AC, but your phone charges on DC. To charge a phone, all you should need is a simple "USB car charger" which just steps down the DC voltage from 12V to 5V. – Nate Eldredge Feb 14 '19 at 16:21
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The first thing I'd do is to get a multimeter and check the voltage you're feeding into the inverter. Is it one of the sort that plugs into the lighter socket? If so, check the voltage between the pin at the end of the socket and the ring on the outside. For a conventional car it would be 12v with the engine off, and either 12v or around 14v with it running (depending whether it has a voltage stabiliser in that circuit) - I'd assume a hybrid would be a consistent 12v.

If that's fine, try plugging in the new inverter, but with the multimeter set to current and wired in inline - this will allow you to measure the current draw of the inverter - check that's within the spec allowed by the device.

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  • No, a 12V battery is more like 12.6V when open circuit, 13.5-13.8V when float charged and perhaps even over 14V when quick charged. – juhist Feb 13 '19 at 18:06
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Are you sure your 12V battery is healthy? A Prius starts its engine with the high voltage battery, needing the 12V battery just for booting up the computers. Needless to say, computer boot-up doesn't require a perfectly healthy battery. It may be possible that the 12V battery is dying, causing various kinds of voltage spikes on the low-voltage 12V electrical system in the car.

You won't be measuring voltage spikes on a multimeter, unless the multimeter can detect and store a momentary maximum voltage. You would need at least a digital storage oscilloscope to do that.

8 years is about the typical lifetime for a 12V battery.

The car electrical systems usually tolerate some amount of voltage spikes, but if you let the situation go to the extreme, it is even possible that some expensive electronics in your car will be damaged!

Please now do a health check for the 12V battery, or even replace it entirely based on its old age.

Oh, and poor connectivity to the 12V battery may also cause the symptoms. Verify all of the wiring if the battery appears to be healthy.

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  • Is checking the 12V battery something I can do on my own? – Sickest Feb 13 '19 at 21:54
  • @Sickest You can check the voltage on a multimeter with the car at rest (should be 12.6 volts after letting it rest for enough long), but load testing the 12V battery is something that only professionals should do with specialized equipment. Be sure to check the leads of the multimeter are in voltage measuring mode, not in current measuring mode! – juhist Feb 14 '19 at 17:08

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