How to know whether it's a 6 cell or 9 cell laptop battery
Most laptops use Li-ion battery packs. The voltage of one cell is 3.7 volt and it's capacity around 2 Ah. So, take the battery out and read it's specifications. Divide it's voltage by 3.7, or 3.6/You should get a whole number.That will be the number of series connected cell groups. Then divide the Ah's by about 2Ah. Again you are looking for a whole number.That will be the number of parallel cells. If the specifications show Wh instead Ah, just divide the Wh by total battery voltage to give you the Ah.
You can Google the model number of your laptop to see full specifications. So, you can find battery information (cells number) in that specifications.
For example, my laptop is Lenovo Thinpad X260 Core i5. I will Google " Thinkpad X260 Core it full specifications"
If the battery is internal, read the system specs to find the information for the battery.
If the battery is external/removable, look at the battery. It will usually say on the label. 9 cell batteries are also noticeably larger than 6 or 4 cell batteries.
This video shows an example of the difference.
Most laptops have either 6 or 9 x 1850 lithium cells in the battery assembly. The easiest way to tell is if the battery case is roughly flat or roughly triangular in cross section. The smaller flat pack has 6 cells and the larger one has 9. A very few small laptops may have only 3 cells, but this is very rare. Some laptops have the option of using the smaller 6 cells or the more bulky 9 cell units