During daylight it is minimal. Vehicles can still drive during the day depending on the effect of the battery light and why the battery light is coming on. The battery light might be coming on because the fan belt is broken and you will see the temperature gauge going up because the same belt might be driving two pulleys.

CHECK

Check the pulleys, fan belts and the alternator to make sure it hasn't seized. You also need a multimeter to check that the battery is receiving charge. A battery light coming on and off requires a check of the charge rate. The charge rate must be checked when the battery comes on especially if you're about to do a night drive. Any battery light, even during the day, may still cut the motor out after a period of driving. Even during the day, the battery is being consumed of power by the electronic ignition, the fuel pump, the radio, the heaters, the air conditioning. All these things require power and if the battery isn't receiving the charge from the alternator then the battery will become so low that the ignition system won't operate. The charge rate should be on the battery poles between 13.8-14.2. Most batteries do not receive this type of charge. They receive something like 13.5-14.2. If it receives 13 volts at idle, this is a problem. If you raise the idle and it is still 13, this is still a low charging alternator. It will affect the battery and it needs to be rectified. The problem is in the charging system.