If there is sufficient memory in the tablet and the update still doesn't work, then the device may be improperly configured. In this case, a factory reset may be required. Check out the troubleshooting page for more info.
There are many possible causes for the issue your tablet is facing. It could be a result of a dead battery, a broken charger/port, or even something as simple as a frozen screen. It is very likely that the problem can be solved easily. Refer to the troubleshooting guide for more information.
If a scheduled factory update fails to initiate, the device could be low on memory. Some files, apps, pictures or videos will have to be deleted in order to make room. If that doesn't help, refer to the troubleshooting page.
If the battery is no longer holding a charge, it may be time to purchase a new one. The A909 takes 3.7V 4000mAh batteries. If the battery is completely depleted, charging it through the USB might not work. AT this point, only plugging it into a wall socket will achieve any results. More information is available on the troubleshooting page.