Alternator Pulse

If could be too much field current, to too low of rpm for the alternator and pulley (hopefully you still have the old alt and pulley), to one of the windings or diodes is out of commission.

Do you have a multimeter?

With a multimeter, the battery circuit restored, and a good battery we can diagnose it.
Then if not something seriously wrong, you can decide if you want to live with or try ot address it.