I have two Dell laptops. A newer Vostro 3500 for daily work, and an old Vostro 1000 as a backup. Both of them died last month, right in the middle of an online course.
1. Dell power adapters die often. Keep a spare on hand.
2. Dell power adapters come in two flavors, 65 watt and 90 watt. Upgrade all adapters to 90 watt versions.
3. Lithium batteries in backup laptops need to be charged regularly.
4. The cells in multi-cell lithium batteries can short out. If a Dell laptop boots up and says "Cannot charge this battery" or "Cannot identify this battery" there's a good chance that the battery has failed. Best option is to remove the battery and run the battery-less laptop from a 90 watt adapter while you wait for a new battery to arrive.
5. Carbonite automatic online backup works. It lets you retrieve your files when your computer dies.