Low Battery Indicator monitoring battery for arduino

My arduino is using a 5V battery as a power supply.
I would like to know if i can use the arduino to monitor the 5V battery
(give out warning if the battery drops below 4V)
Will the arduino still work if the 5V battery drop below 4V?
Thanks

How is the battery connected to your Arduino?

Will the arduino still work if the 5V battery drop below 4V?

If you have an UNO: probably not, at least not reliably. The curve on page 316 of the datasheet shows that the minimum voltage for a 16MHz crystal is around 4.2V.

pylon:

Will the arduino still work if the 5V battery drop below 4V?

If you have an UNO: probably not, at least not reliably. The curve on page 316 of the datasheet shows that the minimum voltage for a 16MHz crystal is around 4.2V.

Yeah but there are lots of folks who run a 16 MHz AVR processor on 3.3V.

I would like to know if i can use the arduino to monitor the 5V battery (give out warning if the battery drops below 4V)

1- Use a 9 or 12V battery...
2- Make a Voltage divider.
3 - Sense with Analog input.
4- No problem!

Measure Vcc without external components or dedicating a pin for the purpose:
http://code.google.com/p/tinkerit/wiki/SecretVoltmeter

The way I read the speed grades curve, 3.8V would be the minimum for 16MHz, but as Coding Badly points out, there is a lot of anecdotal evidence of good operation at 3.3V.