What is the difference between 3 cells, 4 cells and 6 cells battery

I am going to buy new laptop but there is some confusion in battery capacity.

I found that 3 cells battery backup is good than 4 cells battery laptop but I read somewhere that more cells means that good battery backup.

Hence let me clear what is reality and how can I check that battery backup is good by reading specifications.

The number of cells by itself does not have a lot of meaning, unless you are comparing cells with similar characteristics - in which case more cells means a heavier battery and longer runtime.

Batteries are typically measured in milliamp hours or - better (milli)watt hours. If you are comparing batteries you want to compare watt hours - if you have a battery spec with milliamp hours, multiply this figure by the voltage to get milliwatt hours. To convert milliwatt hours to hours, divide by 1000.

That said, you would be better off looking at the quoted run-times for each system rather than directly trying to compare batteries - runtime (for a given task) is not only a function of batteries, it also depends on the kind of CPU and other things - newer generation CPUs are generally more efficient then older CPU's and Intel CPUs are more efficient then AMD ones. [ Also, you get different classes of CPUs - CPUs for ultrabooks will typically give less performance, but use a lot less power than their higher current draw cousins in the same generation ]

I do note that some laptops provide "extra runtime" batteries, which would typically be double the number of cells to their standard batteries, with the corresponding increase in weight, size and runtime.