?Replacement batteries are much cheaper now but this is worth doing
This actually applies to any device that uses a Lithium type battery. Some of this will apply directly to those devices but differences in hardware or software may limit that. The batteries work the same but the stuff they connect to is going to control everything.
If you have a laptop (or other device) powered by a lithium battery you will notice that over time the useful run time decreases. Eventually your laptop will run for a few minutes at most then shut down. So the first thing you will get told is your battery needs to be replaced, and most of the time that will be true. However, sometimes the battery is fine it just needs to be recalibrated.
On a typical laptop you should get two years of use out of it without it loosing much capacity. I actually have a laptop that has a 12 year old battery that holds full rated charge. I've had a new laptop that the battery was suspect after about 6 months but was fine. And I've managed to get some dead batteries to come back to life. There are no secrets to doing this, you don't have to buy anything, and you just need to do a few simple things. Basically think of this as battery maintenance. It's free so that has to be cheaper than the alternative which is battery replacement. If you have already had to replace the battery then you'll be able to make the new one last.
A lithium laptop battery isn't just a battery, there is actually a microcontroller that manages how the battery is charged and this is called a BMS or Battery Management System. The reason they use a BMS is that to properly and safely charge a lithium battery it needs to be charged at a certain rate and finish charging in a certain way.
First thing, we need to know how a lithium battery likes to be treated. This is pretty simple. You shouldn't use more than about 40-50% of the battery capacity. That doesn't mean you can't, but you definitely do not want to drain the battery dead every day. So use the battery and when it hits 50-60% on the meter plug it in if you can. Second, a lot of people will use the laptop much like a desktop and leave it plugged in all the time. This can be as bad as draining it too much. The battery does need to get 'exercised' or used on a regular basis. So at least once a week you want to use the battery. And about once a month you want to use it to the point where it runs out of charge. This monthly deep discharge helps reset or calibrate the controller or BMS. This is the one time where it is a good thing. Normally you want to avoid this at all cost. So the bad things are a lot of deep discharges or none at all. It's a short list but if you think about it that is all you can control.
What if your battery really isn't that old but the meter says it is acting like it is? Do I have to replace the battery? Well this is one of those times where a bit of luck can save you buying a new battery you don?t need. That BMS system also works with another system that is an information and control system. There are several names for this such as HCI or Hardware Control Interface (Toshiba Laptops). There are other names but basically this just lets your laptop hardware talk to your operating system and vice versa. Sometimes the battery is fine but what talks to it isn't accurate. So it will be telling you the battery is low or is bad when it still has lots of useful life. When a lithium battery actually goes bad it will be one cell inside the battery, out of the 6 or more cells inside. The BMS and other monitoring stuff have no way of knowing it is only one part of the battery so it can't compensate and say the entire battery is bad. The battery will also lose a bit of capacity with each charge cycle. Since these systems are not really sophisticated they will after a while be out on the accuracy.
To calibrate or recalibrate you need to do a bit of research. Each manufacturer will have different systems. Some will actually have a reset button on the battery. Some will use calibration software and other will use a special discharge/charge cycle. My Compaq uses the button and software, one of my Toshibas uses just software and another uses the cycle. When you do the recalibration it forces the system to measure the discharge rate and the time. When complete it then knows the new value of how much time or capacity your battery has left. Sometimes you will find that the battery still has plenty of life left. And other times you will find the battery does need to be replaced. Replacement batteries are much cheaper now but this is worth doing before you have to spend money.