Bummer, test it by fully charging it, don't use it but turn it off and let it sit a few days and see if it's still charged. I don't know what type battery it's using, but yours might need replacing.
Lithiums with at least 60% charge are supposed to last for months in storage. I have a big one that hasn't been used for about a year and it is holding up fine. But if the charge is allowed to drop too low, the lithium batteries will self destruct in storage. I have one that starts beeping when the charge gets low, telling me to charge it back up.