The two ratings are not the same.
Wh is Watt-hours. A Watt is voltage x amperage.
maH is milliamperes per hour.
Now, let's do the multiplication.... 4800maH is 4.8aH, or 4.8 amps per hour. If the battery is rated at 11.1 volts... and wattage is voltage x amperage... that would be 53.28Wh. So, the two batteries are not equal... the one at Dell is probably 4400maH, and the one on Amazon would be 53Wh.
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No. It's not exactly the same.
watt = amp * volt
In your case 4800ma at 11.1v is 53.28W