My battery is not getting charged beyond the 98% mark. I know battery losses maximum capacity with time but my question is ideally isn't it supposed to show 100% charged but actually get only 98%? In my laptop it's showing 98% and not going up no matter for how long I have it plugged in.
The complications this question presents are so large, they cannot be covered without a full Physical breakdown of the pack and analisis of the Cells internal to the pack, the charge curcuit, the "info" curcuit , and method used in the info curcuit , and any proper or improper balancing and cut-off (protection curcuit) via all of that.
Lets try and keep it simple (like that's gonna happen).
If the battery is old, it is probably not as well as it once was, If the battery was a cheap knockoff , not only could the cells used in it be short lived, but the curcuitry used in it could be off by some, or even outside of proper specs and dangerous.
The most the user can do is determine if the battery runs the device for at least 50-60% of the time it did when it was a good battery, or the battery is no longer good, nor safe to use. The actual Industry standard, and specs would say if the battery does not hold 80% of its original capacity it is bad, but I am recognising that some people will use a bad pack for a lot longer than that.
The user could guestimate the quality of the internal cells, the exposure to heat (and extreeme cold) the treatment it gets via the charge curcuit, to determine the overall quality of the pack. Then guess the age of the internal cell items, and figure its life. Only Premium Li-Ion cells used in the best conditions, with the best charging alogrythm, will be "good" cell items for longer than 2-3 year time. If the cells are junk, the charge is whatever, if the cells were not balanced, and it is aged 2-3 years, then by default it is probably bad. The ammount of total capacity the cells can hold , and the ammount of time that the device can operate, will also tell that.
While not charging to "100%" might indicate that the battery and cells inside the pack are no longer good, it would not prove that factually, unless all the other factors are known, or the cells inside the pack are tested.
1) li-ion batteries charge using a specific alogrythm CC & CV , and variations of that , that are similar. A 98% charge battery by voltage reading, would be so close to fully charged , it would be a waste of time to worry about it. On the other hand a battery that will no longer charge to 100% Voltage or maintain the charge for time, when it is not being discharged, would indicate a battery that is bad. Li-Ion batteries that are bad, are also unsafe. Again the number showing does not define that one way or the other, the actual state of the cells does.
2) li-ion batteries can use Curcuits that determine charge based on voltage, or current. The current based curcuit would never be able to show an older battery as having all the current it originally had, when the batteries do age, and loose capacity over thier lifetime.
3) Depending on the safety cutoff , and its design, a battery may not show a full voltage, without the pack applying a full and proper Balancing of each cell (or parellel teams) in the series pack. Not all laptop charging, or battery curcuits would apply a full balance curcuit. any single sets of cells in the pack that are weaker than the others could effect the percieved charge level of the pack. This would not factually determine that the pack was bad, or that any cells were bad. Depending on the curcuit, it could just indicate that the proper cell protection methods (voltage cut-off) of overcharge are used, even though an imbalance (voltage from cell to cell) might exist.
4) Charge curcuits properly designed will charge a battery (actually each cell) to the proper voltages , and Stop charging, this is a good thing. A charge curcuit that continues to charge even if the cell does not reach full voltages , is a bad thing. In even proper charging there can be some voltage drop when the charge is no longer being applied, that of itself is nothing to worry about. Even it reading as low as 90% IN USE after a full charge could be completly normal.
5) Many of the info curcuits that determine the current that goes in and out of the cell, and are wrong 1/2 the time anyway because the cells change over time. These little brains inside the whole pack can be reset , by a full discharge and recharge of the cell, wherein in a few weeks they will be off by a bit again anyways. If it was using this type of detection, you could run the battery down, recharge it, and run it down again, and recharge it. That would re-calibrate the curcuit in there, and do little else.