No idea where you get "oms"?

KRM02 has got the right idea. My '98 has sat for weeks & the pretty fresh battery still read 12.16 volts. When the key is switched on that dropped to 11.80 volts. Quite obviously charging, after sitting so long & on high idle, it read 14.36 volts.

IMO if you "have a short somewhere" you usually find out about it pretty quickly, especially in the large wires between alternator & battery. Shorts will ultimately pop a fuse/fusible link or smoke the wire until it burns out. More likely is a bad terminal or connection, that produces high resistance. This can fool a voltage regulator, acting like a fully charged battery.