Can you check the specific gravity of the battery? It sounds like it's only partially charged. A fully-charged battery will have an open-circuit voltage of 12.6 or more. Put the battery on a 5-10 amp charge overnight and check the S.G. in the morning. Each cell should have a specific gravity of 1.265-1.300, with no more than a 25-point difference between cells, the lower the difference the better.
A fully-charged sealed-top battery which cannot get a specific gravity check should have a MINUMUM terminal voltage of 12.5 - - - -12.6 or more is better.
Once you're sure the battery is fully charged, start the engine and run a jumper lead from a battery voltage source such as the big charging output terminal of the alternator to the field terminal. The voltage should jump up to 14 volts or more if the alternator is OK.
Jerry
