Suggestion: Low-power mode

[Twister-UK]

Having an in-car charger is very beneficial, and you won't need to worry about power then.

You still might, if you're in an area with genuinely bad cellular reception (as opposed to the client merely thinking there's no network...), and the combination of active screen, CPU usage, GPS, and maximum radio TX power means the phone is sucking more out of the battery than the charger is able to stuff back in.

If your charger can't keep your phone charged while in use, you need a better charger.
Basically, some chargers only give 0.5 amps rather than the full 1 amp. See the link above.

Remember though that a (properly designed and functioning) device will only pull as much current from the source as its power supply circuitry allows, so simply connecting it to a higher capacity charger isn't always a solution.

[Twister-UK]

Remember though that a (properly designed and functioning) device will only pull as much current from the source as its power supply circuitry allows, so simply connecting it to a higher capacity charger isn't always a solution.

That point is irrelevant. Most if not al smart phones can an will take advantage of having a 1, 2, 3, or even 4 amp charger.

Oh, it's anything but irrelevant. Some, perhaps even many, recent phones can take advantage of higher current chargers, but to suggest that most/all do is incorrect.