Hi mlke03,
There aren't many batteries that will supply 100 W,
except of course motor-car starter batteries.
So i am going to assume you mean them.
You can purchase 100 Watt 12volt lamps,
made for motor cars.
They are actually a little more efficient than
higher voltage lamps.
A single motor car battery would run a 100 watt lamp
for about three quarters of an hour before its charge
reduces the output to a mere glow from the lamp.
I reckon you would need five motor car batteries to
light a 100 watt lamp acceptably for twelve hours.
Unless i am mistaken,
and you really mean that you want it to turn on and
off every 12 hours.
Also if at all possible i need this light bulb battery
circuit to contain an automatic timer that can turn the
bulb on and off every 12 hours.
This is of course possible,
a timer could be made to turn it on, and then off again,
it could do that every twelve hours.
But i think you mean the lamp to run for twelve hours,
then to be off for twelve hours.
That would mean your batteries would have to be charging
for the twelve hours the 100 W lamp is off.
If this is for illumination during the hours of darkness
then i suggest using a strip lamp, maybe a 20 or 30 watt
unit would give similar light output. (needs small inverter)
Also consider using a PIR detector, or maybe two, so
that the lighting is only on when needed, then you
might be able to get away with only one car battery.
Most PIR units are low voltage, the mains units usually
have a small 'transformer-less' supply built in, you
could check their working voltage, varies a bit, i have
found some at fifteen volts, and some at nine volts.
The dearer ones often have a light sensor which turns
them off in the daylight, so maybe you could use that.
Best of luck with it, John