There are several things you can do to make your battery last longer:
Choose the right battery. Under the same use conditions, a lower capacity battery will wear out faster than a higher capacity battery because it has to be charged more often.
Use the notebook's power saving controls to reduce battery use in your normal day. For example, turn the Bluetooth off if it is not needed; reduce the screen brightness when conditions permit.
Avoid exposure to extreme temperatures. If the system is exposed to extreme cold or hot temperatures, allow it to warm up/cool down before use and before charging.
Contrary to last decades' batteries, modern lithium ion batteries do not need to be fully discharged to maintain health.
All batteries wear with use and time. When you find the runtime is no longer satisfactory, it may be time to purchase a new Dell battery.