basta sa multi tester, while the engine is not running, voltage on the terminals of the battery should be atleast 11.1V

while the engine is running, it should be 12.1V-14.5V depending sa loading(buhay na accessories)

if below 12V, di na kumakarga ng maganda ang alternator...madidischarge na battery mo.pagawa mo na yan!

if above 14.5V alternator mo--sisirain nyan battery mo, worst case--sumabog. maaring sira na ung regulator/IC-regulator ng alternator mo.