Battery light comes on while driving

need vechicle model type year.have battery checked.battery cables could be faulty.if all is good. have ECM and BCM checked out.if they go bad they will drain battery.

If you turn key to START position, what is the sound, is it;
1. no sound at all means maybe starter problem.
2. only heard Tik sound means starter problem (you can add relay but it will still happen in future)
3. crank sound but not start means battery weak.

You can also try to move gearshift to N instead of at P position before turn key to START. if it work mean your car safety switch at gearbox not know which gear you're on.

Battery dead in the morning Ricks Free Auto Repair Advice

This is easy to test but you need a multimeter. Connect the multimeter to the battery and run the engine at a fast idle (say 2000 rpm). You should get a voltage reading anywhere from 14 to 15 volts if the battery is fully charged and the alternator is working. If the reading is around 12 volts, then the alternator is not working.

It takes a special tool to reset the SRS on your MB. You can recharge battery as you normally would.

Muriel-sounds like you do not drive a lot, so that is probably causing a problem with your batteries-a battery is like a water tank, it starts out full, and it drains when the car is not running due to loads imposed on it by the radio memory, computer memory, and other things. If the drain is long enough (car sits) the batteries' ability to 'recharge' is diminished due to the conventional construction of a standard battery. A normal car battery can only be discharged a few times and come back-if you do a lot of short trips, and it sits long period of times, that is brutal on a CONVENTIONAL lead/acid plate battery. You should seriously consider getting a deep cycle battery-they are usually used in Marine enviornments, but can be used in cars (I have an Optima Yellow top in my Jeep, it is not driven much, and sometimes is only used for short trips). While these batteries are pricy can be found for about $200 or less) they can easily last 8-10 years and they car be fully discharged hundreds of times and they come back fully when recharged-ideal for your circumstances.

this is assuming the dealer knows what they are doing...after the car sits overnight, the battery should read 12.5 volts. when first started. it should read close to 15 volts at the battery AND at the large post on the back of the alternator-it should gradually drop down to around 14+ volts, and should stay close to the even with the lights and heater fan running ar full blast. if it is doing this, your driving circumstances dictate you get a battery more suited to you driving habits.

this noise is the abs trying to sort its self out it will stop in a short drive
find out why the battery went so flat as well,,,,,if you knock a battery out that flat it may not be any good at holding its charge any more,, and the car will take a long time to recharge it,,,if ever? try hooking the battery up to a mains charger,,, you dont need to remove it from the car if its only a small charger of say 5amps or so,,but it will need a fuw hours to fully recharge the battery,, to work out just how long it takes a 40amp battery will take 8 hours at 5 amps to fully recharge it
40amp divid by 5amp = 8hours,

it realy sounds like you have knocked the battery flat try to recharge it for a fuw days on a home charger off the car if poss if not poss that should still charge up but it takes a little longer to fully recharge the battery up but it will take at least two or three dayes to fully recharge it the way to work it out how long it should take is this,,,a 40amp hour battery will take 10 hours to recharge at 4 amps thats its max charge too?
or devide the amp hour by 10,,,ie: 60amp takes at 4 amp =15 hours charging,,,but it can be charged at 6 amps then its only 10 hours,,, i know,,,boring huh?

The FuseLink is blown. It is a 100 AMP in-line fuse on the red wire from the alternator.

Sounds like the car was running on just the battery. Recharge the battery with a plug-in battery charger, then see what happened to the charging circuit--alternator, drive belt, blown fuse--loose wire. This should have set the check engine light.