Bats don’t lay eggs while birds are egg-laying animals.
Bats have teeth while birds don't, birds use their beak to pick the food and eat.
Bats are nocturnal animals while birds are not.
The structure of the wings of bat and bird is also different.
How are bats and birds different?
A bat is a flying mammal that, apart from its large wings of membranous skin, resembles the mouse. During the daylight hours bats generally roost head downward in dark caves or deserted buildings, then they come forth at dusk to hunt for food during the hours of darkness. Where large numbers of them roost in one place, there is a repulsive, mousy odor. In some caves bat manure has built up into layers of considerable thickness, providing a valuable source of fertilizer.
Birds are warm-blooded, feathered vertebrates and are oviparous, that is, egg laying. Particularly notable are the great numbers of birds of prey (Heb., ʽa′yit) found in Palestine, including eagles, hawks, falcons, kites, and vultures. In their search for food these birds rely on their powerful telescopic sight, rather than on their relatively weak sense of smell.