today my mac didnt turn on, i plugged în and turned on then i saw 0% battery. Why? At only 350 cycles and 2 years.
The battery status of Poor indicates that something isn’t lining up in how the measurement circuit sees the voltage profile change.
The mAh are all estimates / derived / statistical numbers and the only thing the system can really measure directly are voltage - current in - current out and estimated wattage of the CPU. When those 4 values are not aligned or our of what the “model” predicts - you get a Poor / Check Battery / Replace Battery status.
If I didn’t see the “poor” I would say you probably are fine. Also, if you get no charge when there should be charge - examine the pins and cords and cables that are external and then seek service. Make sure you have a great backup in case you can’t turn on the Mac again. Also, once you’re backed up, you might reset the SMC one time (or once every 3 months) if you haven’t recently. The SMC measures and integrates the voltage / time measurements to derive the mAh so it can get stuck and need a restart on occasion or when you see something amiss like you see now.
If none of these work, there's a hardware failure that could be a cable disconnected or a part or two that need to be swapped.
There is probably a dead cell / pack that disables the battery. Since it’s a balanced setup you are going to have to replace it. Be sure to check the case for swelling