Originally Posted by
ChargersFanInCO
Wrong. The BATTERY provides power to all your devices even when the vehicle is running. When your alternator fails while you're driving down the road, what happens? If the idiot light doesn't come on, you have no clue until everything starts to go dim. Why is that? Because you were getting all of your electricity, including power to your fuel pump, cops, etc from your BATTERY. Disconnect your battery when the truck is running, and what happens? The truck DIES. Why would that be the case if the alternator is powering everything? The alternator requires battery power to run itself, through the field wire!
Also, the difference in cranking power is night and day between a 540 and an 850cca battery. Especially when it's cold outside. The starter turns faster, and stronger. That little 540 is supplying power to a lot more than that starter when the key is turned. A LOT MORE.
Well thats not the batts fault if the Alternator dies then your batt dies. You could have a batt doube the size and it will still do that. But when your truck is running as it should you should be able to get all the power you need from your alternator. I could understand if you was running a couple of thousands watts audio system and you drained your batt whilst driveing but as long as your alternator can supply the needed current to charge the batt back up then having a bigger batt wont help. Also the starter wont turn faster with a bigger Amp batt as it's still only 12v but it will def be able to turn for longer. Also the starter motor only pulls the current it needs and fitting a bigger batt dont mean starting quicker. If the starter motors pulls 200amps at ignition then thats the max it's going to need. No matter if it's cold or hot out. When it's warm you may find it only pulls 150amps.