Grand Voyager 94

Hello everyone
I have a small problem with a Grand Voyager 94, what happens is that a couple of days ago I marked on the board the light of "Check Engine", immediately lead her to review her in a workshop, they tried to scan to see what the problem was and they could not, arguing that her Scaner performed an update of her software.
As soon as the signal turned on the board, check all levels and only a bit of antifreeze is missing, which if I worry is the level of the oil that was in the minimum and already very black of Echo had scheduled to do the internal washing of the engine and the change of oil the weekend.
Not being able to scan, the mechanic recommended me to make it washed and the change of oil and that arriving home disconnect the negative battery terminal all night, if the problem was the oil would be erased the warning and all normal. Connect again in the morning and start without problems, the notice still appeared. I took it to school and half of my way I marked the "check gauge" and I realized that the battery level was in the minimum reached school, it appears, turns it off and when trying to light it no longer left me.
I hope you can help me.
Thank you so much

If the battery does not load and circle the Asta vehicle that you run out of battery is for the alternator has a failure.
If your mechanic told you that the oil was changing and that you would remove the battery terminal that your car would argued alone, uffffff

changes the mechanic and that the alternator will see if the fault is there.

I do not think the problem is the problem, the check Engine only throws failures of the injection system, if the vehicle is fine but the light appears is usually temperature or oxygen sensor, but the battery is another story to put another or load that you have and measures how much the alternator loads the alternator