Rene, you have no way of knowing the state of the cells any more than I do. The charger will not respond if they are below whatever voltage the battery management system is set to. They need not be flat and are unlikely to be flat. They have just fallen below a threshold. In all likelihood they can be brought above that threshold so that the charger can bring them back up to full voltage. I’ve done it amore than once with laptop battery packs that have not been kept charged and restored them to full use. My advice to Pirots stands – that he should go to a battery specialist. Scare-mongering is not helpful.