It depends on the settings of your ipod.
You should be able to plug it into his laptop to charge it without having to do anything else.
If itunes opens when you plug it in it may ask if you want to sync it with his itunes so just say no.
Your ipod should still appear in his itunes and if you change the sync setting from automatic to manual you can just plug it into his itunes, drag songs onto your ipod and disconnect without losing any of the current music you have on your ipod.
The main thing is that if you connect to itunes don't allow your ipod to sync automatically as that's what will cause it to wipe off your music.
Just make sure the settings in itunes for your ipod is set to sync manually. There will also be an option in there somewhere to only open itunes when you want to and not to open automatically when it detects an ipod connected. It's handy for charging your ipod without having any pop ups from itunes that you mightn't understand.
Hope i helped
Any more questions or if any of that was unclear i'll add more
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