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Short answer: not quite right.
Charging overnight with the device off should not be a problem (see calculation below that shows just over 3 hours).
By "more power hungry", ziplinq the company is saying that the average amount of current used by the 4350 when charging and syncing is greater than for example the 2215 (i.e. closer to or more than the USB specification)
The 4350 battery capacity 1560mAh. The "h" is important, it stands for "hours". mAh is milliamp hours and represents the capacity of the battery. Without the h it is just mA (milliamps) and represents current draw (my term).
The power specs of the 435x:
Removable/Rechargeable 1560 mAh Lithium-lon user swappable battery. Estimated usage time of fully charged battery up to 17 hours (no wireless, no backlight).
This means that the 4350 at a *maximum time* (no wireless, no backlight) will discharge it's 1560 mAh battery in 17 hours. This represents a *minimum* "on" current draw of 1560/17 = 91mA. Compare that to the 500mA that the USB can supply, which means that when the device is on (but presumably not running anything), there is 500-91 mA left for charging the battery assuming that the power control circuitry in the 435x directs the current in this manner.
It's ok if you don't follow that, but follow this: mAh can be used to calculate charge or discharge times if you know the mA of charging or discharging.
Comparisons of charging cables is done by the amount of current that the charging cable can supply (but ultimately limited by the device charging circuitry). You could compare the 500mA of the USB with the AC adapter "output current" of 2A.
AC Power: AC Input: 100~240 Vac, 50/60 Hz, AC Input current: 0.2 Aac max; Output Voltage: 5Vdc (typical), Output Current: 2A (typical)
Note that 2A is the same as 2000mA.
This means that if there is no current limiter in the device, and the device is off (drawing no power) the AC adaper will charge the 1560mAh battery in 1560/2000 hours, or 46.8 minutes. A USB charger limited to 500mA will charge the battery 4 times slower, or 3.12 hours.
Note that if the device is on, it will take that much longer to charge the device, and it has a greater effect on the USB charger than on the AC adapter.
(if you are reading this far, the following is just extra bonus calculations)
If the device is drawing 100mA, the charge times are:
AC: 1560/(2000-100) = 49.2 minutes; USB: 1560/(500-100) = 3.9 hours
If the device is drawing 300mA, the charge times are:
AC: 1560/(2000-300) = 55.0 minutes; USB: 1560/(500-300) = 7.8 hours.
But again, this is assuming that the USB charger output is limited to 500mA. This is of course the specification of USB, and may be different for chargers with USB output as opposed to USB data ports (Belkin, for example, specification on it's Car charger with USB port is 700mA). Note that all of this is very likely why the iPod is charged over FireWire, as the 6-pin FireWire cable can supply much more current than USB).
Congrats! You got to the end of this message!
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