It's because the total voltage of the pack isn't what it set in the charger.

14,8V is 4S LiPo.

You can use the charger in a few charge modiï. Charge and balancing charge. Balancing charge is almost mandatory for us.

If you program 4S LiPo and 2A, it will charge any battery that has a voltage between 10.8V and 16.8V.

With balancing, the individual cells are measured, and if 1 gives a too low voltage, the charger won't start either.