How to do you read the alternator gauge?

The Way your gage reads, it is over charging.
How long was it running when you took the pic. Should go to center after 5 or so min's, on good battery.
Or you might have high resistance some where in the circuit.
It could be lots of common things, in the wiring, specially in the bulk head connections.
Is the batt good, how old is it. ??
Check all your connections, use dielectric grease on batt connections
Dave