Charging questions

[richelesro]

When plugged into the car, the phone doesn't charge if I have navigation on. More accurately, it seems like the charge coming from the adapter isn't enough to offset the power draw from the navigation. I've tried three chargers, all of which advertise 850mA, but none of them work. Is anyone else having this issue?

Also, is there an app to find out what amperage is coming through the charging cable? That way I could find out what's really getting to the phone.