I have been using a battery charger that is around 30 years old. Seems
like it has been working well the last few years, but I wonder if
getting a new one will give me a better charge. Is a battery charger
just a battery charger, or is there a difference?

I, for one, am no expert, but seems to me if it's charging your battery,
then it's charging your battery. The only way a new one will give you a
'better' charge is if it charges faster.

I am pretty sure of one thing though... you'll get replies differing
from this one LoL