Based on this product's specifications, here are some alternatives and similar models
Battery Green Cell for Lenovo ThinkPad T420s T420si 14.4V 3600mAh
Summary description:
Rechargeable laptop battery Green Cell designed for Lenovo ThinkPad T420s and T420si. Nominal voltage 14.4 V and capacity 3600 mAh. Replaces original battery to restore portable power for everyday mobile use, office work and travel. Provides reliable runtime, easy installation and compatibility with specified ThinkPad models.