Hi Bingo and
to the forum.
44V is much too low for a fully charged 48V pack, it should be around 54.6V.
Check to see if your charger has a voltage switch to select your mains supply voltage.
There might be a simple slide switch like this:
If your charger is fitted with one, set it to the 110V setting
(if applicable) by using a small screwdriver or cocktail stick etc. to slide it to the correct position.
Let us know if this rectifies your problem.
Alan