Yes, it is okay to use a laptop without its battery. In that setup, the laptop will then effectively be a desktop PC, as obviously it could no longer be used unless plugged into the AC adapter. However, some laptops are designed to run with Hybrid Power. When under heavy load with CPU-intensive and GPU-intensive tasks such as video editing or gaming, the laptop draws power concurrently from both AC adapter and battery. If the battery is removed, then in those situations the performance would be reduced.  
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DS 07/20: Is it ok to use a laptop without the battery?