That is an important distinction! Since many X240s were sold with a dual-battery setup (internal + external), being clear that this unit only has the external battery prevents a buyer from claiming a "missing part" later.
Here is your updated listing:
Lenovo ThinkPad X240 12.5" Laptop | i5-4300U | 8GB RAM | 120GB SSD | Win 10 Pro
Ultra-Portable Performance for Professionals and Students. The ThinkPad X240 is built for durability and portability. This unit is maxed out with 8GB of RAM and a 120GB SSD, making it a fast and reliable choice for web browsing, office tasks, or schoolwork.
Specifications:
Processor: Intel Core i5-4300U @ 1.9GHz (Turbo up to 2.9GHz)
Memory: 8GB DDR3 RAM (Maximum supported for this model)
Storage: 120GB Solid State Drive (SSD)
Display: 12.5-inch Anti-Glare Display
Operating System: Windows 10 Pro (Fully Activated)
Connectivity: Mini DisplayPort, VGA, USB 3.0, Ethernet, SD Card Reader, and Webcam.
What’s Included:
Lenovo ThinkPad X240 Laptop
External Battery (Included and installed)
Genuine Lenovo Power Adapter / Charger
Used - Fully Functional. This laptop is in good cosmetic condition with some standard light scuffs on the casing from previous use. The screen is clear and the keyboard is fully responsive.
Important Note on Battery: This unit contains the external removable battery only (no internal bridge battery). It holds a charge and functions as intended, though the exact battery life is not guaranteed. The laptop works perfectly on both battery power and the included AC adapter.