iPod classic 80GB 2007 [Model No.:A1238] won't charge from LG usb travel adapter (output 5.0V, 0.85A). It normally charged from Apple 5W USB Power Adapter [Model No.:A1299] (output 5.0V, 1A), and normally charged from macbook USB port and required just 0.5A for charging.
Why it won't charge from LG adapter whose output current (0.85A) actually is between laptop USB port (0.5A) and Apple USB Power Adapter (1A)?
Best Answer
I looked into the amount of current available from a USB charger when investigating how to charge multiple iPhones / iPads simultaneously. Below is something I learnt that might be relevant.
There are several different ways that a charger can "tell" an iPod how much current it can provide - the iPod can't determine this directly. If the charger is a computer, it will communicate this through a data transfer (similar to transferring MP3 file data).
But a simple charger won't use this method. Instead, there are various standards (some proprietary, I believe!) which specify how much current can be provided, by providing certain voltages at the data lines. USB has four pins: one ground, one power, and two data. For example, apparently 2.8V on one of the data pins and 2.0V on another means "you can draw up to 1 amp". See this link for some detail, although I think some of that is out-dated.
I'd guess that the LG adaptor doesn't provide the signalling that the iPod expects. I don't know a way to resolve this, other than to try a different adaptor - sorry.