Why is my DC adapter charger intermittently flashing

The last time I used my DC45 it was working and with charge. When I attempted to use it again, it was completely dead and the adapter charger is now intermittently flashing and not showing solid green (charging). I replaced the battery about a year ago, so should be an issue. The odd thing about this issue, is when I press the trigger switch the charges stays solid green as if it's charging (but it isn't)