No Power with new battery

I have a chevy 96 lumina. The car will only start with the jumper cables put straight on the starter and a ground. The battery is brand new and had it tested to be good also. We just replaced the starter and still have nothing. The voltage out of the battery is 12.6 volts and when the cables are connected the voltage drops to a little less than 5volts. Do you have any ideas to what could be draining the power? Also the battery alone doesn't allow for any of the electrical to work unless you attach jumper cables to the car. If there isnt enough power from the jumping car it will only pulseate, the jumping car has to be reved up to start my car too.

Alternator!

How long does it take the battery to drop to 5volts? I wouldstart checking your battery cables, I assume you used a voltmeterto check your battery voltage, so I am assuming you have one. If the battery is draining pretty fast I would check as much as I could with the negative battery cable disconnected. Put one lead on the negative side of the battery and with the positive side of the battery hooked up I would start checking for voltage at the non battery side of the battery cables (i.e. starter, alternator, relays) if one end of a wire as 12.6 volts and the other doesn't have something close you found your bad wire. do the same thing with the negative cables, make sure the negative battery cable is hooked up and put one lead on the positive side of the battery and check your negative cables, if you want to check to see if the alternator is what is draining power and the alternator is easy to get to then disconnect the negative battery cable and unplug the electrical connector to the alternator and remove the wire from the back of the alternator, if the battery drain goes away then that was the cause, if it doesn't then it's something else you can try pulling relays to try to eliminate the circuit that is draining power

I found that a 60A fuse and the HD LMP fuse in the under hood electrical boxes is causing a problem, if the HD LMP fuse is in the volts to the starter drops to about 5 volts, Then if i add the 60A fuse the volts drop completely, I just cant find out what is causing the problem between the two and i cant find where they are and located in the car on the wiring diagram. Any help would be appreciated.

I have replaced a few fuses also (25,15) that look a little croded also.

Check your connection at the remote jumpstart terminal, make sure you aren't loosing primary power there.

Finally fixed it, it was the battery. It was putting out enough volts and amps but it would fault out when it was put under stress. thanks for the replys

New battery defects are common, maybe 3 out of 100 will have dead shorts inside them. Good thing you found it without replacing 1/2 the starting or charging system.

Always toss in a KNOWN battery when making a diagnosis just to rule a bad battery out. A dead shorted battery will drive you nuts if you never ran into one before.

Bob