Everytime it powers on, use it until it powers off again.
Then plug in the power.
As soon it powers on again, unplug the power, then use it until it powers off.
Repeat until it will not power on immediately.
When it won't power on immediately, leave it powered off and let it charge to full.
What it does is properly calibrate the battery.
Now if this doesn't fix your issue, you do have a dying or dead battery, and it will need to be replaced.
Battery replacement guide is here.
iPod Nano 4th Generation Battery Replacement
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And by the way, i have turned backlight off, and its working for half an hour now
crwdns2934271:0crwdnd2934271:0 harry jackson crwdne2934271:0