So, why this is happening? Every new battery obviously have a 100% of original capacity. However with time as we use the battery for sometime the original capacity is starting to decrease, and even if you charge it to full, it won't be able to hold that long as it used to when it was new.
When the battery is only able to hold no more than 40% then Windows 7 will notify you of that problem by flashing red "X" on your battery icon in the conner of you screen.
Even the rechargeable batteries need replacement some day!
Replace your one today!