Hi,
I have encountered this issue before and have a possible solution for it! If the battery is actually dead, it will need to be repacked by a professional, there is no DIY solution. However, as it is flashing when you attempt to charge it, it is possible that the cells are not dead and have simply just discharged past the point that the charger recognizes. Flashing means the station has encountered an error in recognizing the battery and is often due to the battery being too discharged. Luckily, the cells can be very discharged without actually being dead.
In this case, you can sometimes "jump start" the battery by repeatedly inserting it into the sub battery compartment of the charging station, removing it once the light starts flashing, and reinserting it again until the charging light stays solid. This works because the charger supplies a small amount of power to the battery before recognizing that it is too discharged and stopping each time and these small amounts of power can add up. It may only take around five tries for the light to stay solid, or it could take many more. If you have tried removing and reinserting the battery 50+ times and the light still blinks each time, that means that the battery is likely dead. There may be risks involved with this method and it is not useful for batteries that are actually dead, so do not continue trying to reinsert and remove the battery if it does not work after around 50 tries.
If this method does not work, unfortunately the battery will need to be repacked by a professional. Please do not attempt to repack the battery yourself as this cannot be done at home. Aibo batteries are "smart batteries" that can detect when tampered with and will become entirely unrepairable if you remove the cells without reprogramming the internal board first. There is a seller on Yahoo Japan offering battery repacks for ERS-11X batteries for around $100/¥10,000, as your account says you are located in Japan, that would be your best option if the battery is dead. Do NOT under any circumstances open the battery, this will make it unusable.
Hope this helps and let me know if you have any questions!
