Charge the battery overnight at a 10 amp rate or so, and if possible, check the specific gravity of the acid in the morning. It should be between 1.265 and 1.300 or so on all cells, with no more than a 20 point variation or so. Open-circuit voltage on a fully-charged battery shouls be 12.6 volts or slightly more. If you don't have access to a high-load tester for checking cranking power, disable the ignition and crank the engine for 15 seconds. Battery terminal voltage at the end of the cranking session should be 10 volts or more, while the engine is still cranking. If the battery passes all these tests, replace the alternator, after checking to be sure the charging system wiring is in good shape, of course.
Jerry
