When you charged it and it only took 300mah, did the batt get hot? If not, its prob a false peak - the charger thinks it see the small peak voltage rise and thinks the batt is full so it terminates the charge and its really too early.

Just reset the charger and try again. New batts seem to be bad about false peaking and you might have to do this several times to get a full charge. Some chargers have a peak delay time so you can tell teh charger to ignore anything it thinks is a peak for 10 or however long you think is necessary so the batt doesn't false peak. Unfortunately the Venom charger doesn't have this so you just have to keep resetting it back to charging. The batt should get to ~120F or so when it truly peaks, so until it gets that hot, just keep trying.

As batt gets older it won't do this as much.