What is the best practice for the first use of a Dell laptop battery
With lithium-ion batteries its best to top-up charges and not allow the battery to drop below 20-30% too often. This is due to Dell batteries having a limit to the number of full charge cycles.
Regarding first time use, it's best to allow the battery to fully charge before using it without a charger. This allows the cells to stay active and enables the laptop to calibrate and optimize battery usage.