Originally Posted by VStromNC
I tend to agree with your statement as I am trying to replace my dedicated Garmin car GPS with my new Galaxy S4. I have the Co Pilot App installed with a US map for $9.95. Very versatile and slightly buggy, need to restart every now and then, but has bunch of features. I am using a 12v to USB converter with 2 amp output and I am still noticing that over a course of about an hour, the battery still discharges even though it shows that it is charging. I'd say that although it is discharging very slowly, it is possible that having the display to the brightest setting with GPS mode running, could result in battery draining faster than recharging rate and leaving the phone dead after 1/2 a day.
I am still trying to tweak the power setting.......
I almost gave up using my new Galaxy S4 as a Car GPS due to charging issue. My setup was one of those bullet shaped 12v to USB adapters that you find everywhere. Mine had a dual output- First is 1 amp and the second output is labelled as a 2 amp. I was also using one of those retractable USB to microbus cable.
While trying to Google maximum power (current) draw of my S4, I came across this article and basically, it talked about how the smartphones are now able to sense your voltage and current output including your cable capacity to determine the charge rate. Lot more to it but good stuff.
I changed my retractable USB cable to a high quality shielded type and took it out yesterday. With display on the highest setting and with GPS running, the battery actually started charging using the 2 amp output.
Previously, the battery was discharging with the only difference being the USB cable. I tried the 1 amp output and it started to slowly discharge. My Galaxy S4 AC power supply that came with the phone output is rated at 2 amp and so using 1 amp is simply not sufficient.
I had it our about an hour and worked great and the battery was fully charged.
The article below is really for geeks but interesting reading nevertheless.