It could possibly be the charger. Check to see if your charger wire has any cuts or distortions on it. If this is the case, the charger wire might be frayed and you will need to get a new one. Also, check to see if your charging port is working as well too. It might be blocked by a speck of dirt that won't allow the grooves of the charger to fit into the computer.
If none of these are the problem, your battery is probably not functioning properly. In this case, you will need to replace the battery. Here is a link to a battery replacement guide.
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