To start charging using iMax B6 it need to have 3.5-3.7volts minimum.
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If it has lower voltage then you need try to charge it directly using 5V PSU until it get 3.7-3.8V then use iPod to charge it or, better, charge it with any li-po(li-ion) charger to 30% minimum(or about 3.9V)
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Then try if it start charging in your iPod.
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If iPod powers up when you connect charger, better turnt it off and live it for charging battery.
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Also check temp of it, if battery is destroyed it may overheat, then disconnect charger from device and disconnect battery from PCB!
Hello, looks like you almost answered your own question.
But if you need to hear it from someone else, no problem.
Step by step -
Check -
charger OK
cable OK
battery OK
internal(inside iPod) battery cable OK
on board battery cable connector OK
charging port on iPod(clean it with alcohol!) OK
last one is main board, power controller on it may fail to
Also, here is a iPod Classic repaid guide with pictures -
[[Topic:iPod Classic]]