jerryc41 wrote:
I've read a couple of articles about the negative aspects of charging a cell phone in your car. I've been charging cell phones in cars for years without problems.
1. The USB port doesn't put out enough current.
2. The 12v outlet puts out too much current.
3. If the car isn't running, you can kill the car's battery. Considering the size of the car's battery vs the cell phone battery's, I wonder.
Any opinions?
Yeah, in my Prius:
The USB port was made for an iPod. It cannot charge an iPhone.
The 12V outlet puts out (nominally) 10.2 to 12.6 volts in Accessory Mode, and about 13.4 to 14.2 volts — normal charging voltage — when the car is in READY mode. It puts out a maximum of 150 Watts. That isn't "too much" or "too little" current. Maximum current would be around 12 to 15 Amps. What matters is the output from the charger you plug into the 12V outlet. Most phones require a MINIMUM of 5 Watts at 5 Volts (25 Watts, because Watts = Volts x Amps...). Newer phones with fast chargers or inductive charging can draw a bit more, but 150 Watts should be plenty for a couple of car chargers.
So most important is the *design and construction* of your car charger. If you bought the sub-$5.00 kind found in convenience stores, gas stations, and novelty shops, it probably isn't voltage-regulated and filtered properly. If you find that your phone gets hot when charging in the car, but stays cool when charging on the OEM charger at home, throw away that cheap car charger and get a good one. Low output voltage causes the phone to pull more current, which heats up the battery. Some of the cheap chargers put out only 3 volts.
In many cars, mine included, the 12V outlets won't stay on unless you keep the car in Accessory mode, which requires keys to be left in the car. Leaving keys in the car is stupid unless your car is in a "no crime zone," such as a locked garage! And unless there is a LOAD on the charger in the 12V outlet (such as a connected phone), there isn't significant current draw to cause a battery to drain over night. In cars with keyless remote entry, you're likely to drain the battery from letting the car sit for two weeks without driving it, if you don't turn off the keyless entry feature.
My twins bought a cheapie charger when they started driving. I had already taken both their iPhones in for new batteries, when I called them into the garage one day, put their car charger on a 2x4 on the floor, and smashed it with a sledge hammer. Then I handed them a new one (10-Watt Belkin, I think it was). I got a puzzled look from them, then explained that their phones were dying prematurely because the low power from the charger (3.4 Watts instead of 5 or more) was causing the batteries to overheat from too much current draw.
My current phone is an iPhone 7 Plus from early 2017. I've had it for four years and nine months. It is just starting to tell me the battery is failing. The average life of rechargeable batteries is around five years when you treat them right. So I'm okay with that... My car charger is a good one! I need a new phone case and new battery, so maybe I need a new phone, or at least a kit from iFixIt and a new case. Decision time...