Let's compare 2 situations:
My smartphone is totally discharged. I plug a standard phone charger (standard 5V adapter, with micro-USB, wall adapter), then the battery increases of, say, 1% percent every 10 minutes. You can use the phone at the same time in normal conditions (messaging, but no video), it's still charging. Normal behaviour.
The same smartphone is totally discharged. I plug it on my car's "lighter adapter" with the following devices:
CAR 12V LIGHTER PLUG --> LIGHTER ADAPTER TO USB --> USB-TO-MICRO-USB CABLE --> SMARTPHONE
Then I notice, that even if I use the phone in same conditions as before (i.e. no GPS or other high-current-consumption tasks), while someone is driving (i.e. motor of the car on!), the battery doesn't charge. At best it keeps the same percentage: if battery was 5%, it will stay around 5% for hours, but no increasing charge.
Is the problem:
- the car lighter power 12V adapter that has a current-limitation system (how does this work?)
- the lighter-plug-to-USB car adapter (see picture before)? Do such devices include a current-limitation system?
- something else?
Is there a solution: how to get a properly charging phone in car?