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My 1999 Civic SI has a starting problem .. I have replaced the alternator, battery and starter. It starts about 15 to 20 times without a problem, then suddenly the battery will be dead. Mechanic has checked all ground wires, etc.

 
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It's sounds like a parasitic draw. Means you have a short/open somewhere. Check any accessory wiring that you may have installed. After that I'm at a loss.

 
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is it voltage wise low after the 15-20 starts? put a dmm(digital muti-meter) on the battery and post what it rest on after each couple starts

 
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When the battery is dead, nothing happens when I turn the key, no connection at all. Sometimes it makes a clicking sound.

 
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I assume there is no warning light(s) whatsoever?

To look for high idle drain... with the car turn off and all doors closed, remove ground cable from batt, insert an amp meter, it should read under 1 (one) amp. An high drain mean some accessory is failing (newly installed accessory?) is drawing too much power all the time. The symptom for this is that if u leave your car parked for several days, a week, the batt automatically dies. Good systems should last over a month parked and it will start up after u come back from vacation.

If that's not it, u maybe getting low voltage at the starter. When it doesn't start, hookup a voltmeter directly across the battery, crank it up, the meter should read no less than 11 volts, else probly need new battery. If 11 volts or above, hookup voltmeter across the starter selenoid (inputs to the selenoid's coil), crank it up, again it should read around 11 volts and no less. If prob here there is a prob with the wiring between starter and battery, probly loose ground.

 
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Thanks for your help, turns out it seemed to be a poor ground wire on the battery, though it continued to have a problem for a couple weeks after it was put on, it seems to be fine now (I hope) Haven't been on the forum since ... sorry I didn't reply sooner.