9-Cell battery

If you bought a laptop from dell, the default battery for it is usually just a 6-cell battery. A 6-cell will only last for around 2-4 hours depending on use, but a 9-cell can last up to 4-6 hours. Aside from that, there are several advantages that a 9-cell battery has over a 6-cell.

Advantages of a 9-cell battery:

1. More usage time
It can store more power which will result in more usage time. This comes in handy especially if you're using your computer for travel.

2. Cooler system
Since it's a bigger battery, the laptop will be raised a few degrees, giving space underneath the laptop for more airflow and a cooler system

3. It's Ergonomic
Raising the backside of the laptop a few degrees, people who type on their portables won't have to worry about that flat awkward position anymore.

There are other advantages but then getting a 9-cell is better for the usage of the system than a 6-cell. The only disadvantage I could think of is that it's a bit heavier and it might not look good on the laptop since it's bulkier. But choosing over use-ability and good looks, I'd go for a better performance system than a good-looking one.