A-hr refers to "Ampre hour", a measure of the electric charge.
W-h refers to Watt-hour - the energy of the battery.
Relationship: Ahr multiplied by voltage gives Wh.
In your case, 4Ah X 10.8 volts gives 43.20Wa, i.e. a 10.80 volts battery rated at 4Ahr is equivalent to one of 43Wh as long as the voltage is the same.
(E.& O. E.)
I have a Compaq Presario V5000 that uses a HSTNN-IB17 battery. I have one extra and I just purchased another not realizing the rating. In all three cases, they are rated at 10.8 volts. But the two that I already had are rated at 4.0Ahr and the new one it says 43Wh. So Im confused as to the difference between the Ahr rating and the Wh rating.