from what i have learned, am reaching the following conclusions:
1-if an alternator fails without previous warning, most likely was because the brushes worn out completely;
2-if begins to give erratic "battery off" messages, is that the shaft where the brushes rub has blackened out and there are false contacts.
in any case, means that the alternator has to be removed, replaced, or disassembled and brushes checked for life left, and shaft for blackening.
if brushes still have life, can be used (ideally you have the spares so replace them now).
also, clean the shaft.
if anybody has better solutions and ideas about this, please post.
this is just my approach based on what happened to me.
a link for brushes: brushes are about 14mm; need to have at least 4mm running into the cavity, the rest (about 10mm) is the life available. the measure you find tells the % it still has.
edit: but wait... please read the next post. by now i have learned some things that are worth considering....