Typical laptop batteries last up to 5 years with average use. If you have had a battery for longer than this, you should consider yourself lucky and possibility look at getting a new one.
Most batteries appear to look okay, since you can't see inside them. However, inside a regular laptop battery are normally 6 cells. 1 by 1 these cells fail after so much usage and the only way you can really tell is by how long your laptop can stay on battery for without external power.
Can you replace the cells within a laptop battery?
No, we really would not recommend this, a whole new battery is required.
It is not advised due to the volatile nature of the cells inside. All laptop battery packs are sealed for this very reason. Should a battery cell become pierced it will ignite and react violently. It can be a cheap way to just replace one or two cells rather than the whole battery , but in no way do we recommend this. The other reason is because inside most laptop batteries will be a small PCB controller board, which tells the computer that the cells are ok. Of course, you won't be able to reset this and therefore the computer will believe it is still using 4 cells as opposed to 6!
Where should I get a new battery from?
We can supply you a battery from one of our trusted suppliers. We do not recommend buying batteries directly from eBay, as they can already have failed cells even when they list the battery as "brand new". Of course, a battery with an already failed cell will not last as long as a genuinely new one!
What about the button / coin battery in a laptop?
Most people are unaware that there is another battery inside laptops, which is referred to as the CMOS backup battery. This battery saves the boot up information for the computer and also stores the correct time and date. If you were to unplug your laptop and remove the main battery over night, one might expect the time and date to be wrong, but it won't be due to this backup battery.
These coin batteries vary rarely require replacing but if you have to, it must be replaced by a rechargeable equivalent. It is worth noting that in some laptops they are directly mounted to the motherboard and are therefore not easily replaceable.
If the date and time on your computer is wrong, the button battery may just require recharging. To do this is very simple, leave your laptop on for 24 hours, plugged into the wall. Do not let it go into standby, as this will cut out the recharging of the battery. After 24 hours, the battery should be fully recharged and might save you the hassle of finding a replacement!