It can mean 2 things.
- Your battery is not calibrated right
- You have software running that prevents your battery from charging until a certain level has been reached in order to prolong the lifespan of the battery.
In case it is 1:
Basically it is charged up to 100% but the computer thinks its still at 98%.
Some BIOS have the option to calibrate the battery. If yours doesn't, the following trick will work too (not just for laptops, works for phones and other devices with a recharchable battery too)
First completely drain the battery. Once the battery is drained, turn it back on, and again wait for it to go dead. Keep turning it on until it really won't turn on anymore. You may want to go into the BIOS when doing this because windows will automatically do stuff to reduce battery life such as hybernating the laptop.
Once the battery is fully drained, connect the powercord and charge the battery. Make sure the battery has at least 5% to 10% charge before turning it on, and ensure that you will be able to charge it to the full 100% in one go. Aborting somewhere may cause it to revert to the above behavor. Once the 100% mark has been reached on that first charge, you should be able to use your battery normally charging when you want upto when you want without much issue.
When you charge a phone to 100% and keep it plugged in, most phones will lie to you and keep showing 100%, even though it is actually going through a short 2-5% charge-discharge cycle, so that the battery is not always charging. Windows 10, on the other hand, appears not to lie to you. It reports the true percentage of the battery, at the risk of confusing users. My Surface Pro 3 is showing "95% available, not charging", even though it's plugged in, but sometimes it does actually show 100%. – None – 2016-10-11T02:01:39.603