Handling old laptop battery

If I disconnect the power from my laptop, the laptop shuts abruptly in 5 to 10 seconds. Looks like the battery is gone. However, I suspect some kind of firmware involvement also in this problem. When windows desktop is put under some prompt, then the laptop doesn't die even after removing the plug. So, if I wanted to move the laptop around while still working, I click on shutdown and leave the shutdown prompt as it is. After shifting, I cancel the prompt. So for this method helped in retaining for power for 15 minutes. Let to try beyond.