Based on this product's specifications, here are some alternatives and similar models
Battery Pack HP for EliteBook 840 G5, 11.55V, 4113mAh
Summary description:
Replacement battery pack compatible with HP EliteBook 840 G5. Nominal voltage 11.55V and capacity 4113mAh provide power for mobile work and travel. Designed to fit the specified laptop model and restore runtime for system use, document editing, web browsing and light office tasks. Easy to install and intended as a direct replacement for the original battery.