<div class='quotetop'>QUOTE (zoned019 @ Jun 27 2006, 06:41 AM) <{POST_SNAPBACK}></div><div class='quotemain'>Get the car running, and then disconnect the battery. If it stays running, you need a new battery. If it dies, you need a new alternator.</div>

it's not the best way to check.

some electronics, especially on new cars may go wrong when you do that, also you will have no load on alternator, so that voltage regulator may go wrong.

Turn on headlights, low and high beam and measure voltage with engine off, if it's below 10V - you have bad battery (or underchared). If you start the engine and turn on blower, headlights, audio and have lower than 13V - you have bad alternator.

 

will a optima blue top work in the car? cause i see people with those even though they say its a marine deep cycle battery and not a automotive deep cycle battery

 

<div class='quotetop'>QUOTE (zoned019 @ Jun 26 2006, 11:41 PM) <{POST_SNAPBACK}></div><div class='quotemain'>Get the car running, and then disconnect the battery. If it stays running, you need a new battery. If it dies, you need a new alternator.</div>

That is also a good way to kill a good alternator. Alternators need both a load and a "buffer" in order to work correctly. Without the buffer of the battery (no matter how bad) the alternator will either put out no juice at all.. or try and power the entire car and burn out the diodes