Nikon F100 battery drain. What causes even when the camera is turned off.

I recently purchased a second Nikon F100 for parts on ebay. With no battery door. I replaced it with my 1st f100 door and the camera came to life to my surprise. Over night the battery drain to unusable. I put on the Mb-15 grip and the same thing happened with my rechargeable Lithium batteries. Is there a easy fix for this? I see evidence of corrosion and wonder if this may have been the culprit. Otherwise the camera works perfectly. The shutter does not fire using the MB-15 aux. release.

I The shutter does not fire using the MB-15 aux. release.

Sounds like some kind of short ciquit tome, and if the MB-D15 release does not work , while it is working properly on your other camera, then that may be where the culprid is, in the connector for the battery pack to the camera ..

It sounds like the battery drain occurs with and without the grip, which eliminates the grip and it's connector from the equation. There is, I believe, a second battery (not user replaceable) in the body to maintain settings while there is no battery in the camera. This battery is charged by the primary battery when there is one in the camera. There may be a short in this secondary battery that causes it to quickly drain the primary. Of course, there are many other places that a short could occur . . .

[Think you must have already tested this]: Can the batteries be the problem?

It sounds like the battery drain occurs with and without the grip, which eliminates the grip and it's connector from the equation. There is, I believe, a second battery (not user replaceable) in the body to maintain settings while there is no battery in the camera. This battery is charged by the primary battery when there is one in the camera. There may be a short in this secondary battery that causes it to quickly drain the primary. Of course, there are many other places that a short could occur . . .

I am not sure if there is an internal battery. An internal battery is only needed for the clock and not to retain settings. But the F100 may have the clock/calendar function.

The F100 doesn't have a clock (unless you count the clock in the optional MF-29 data back, which is separately powered by its own batteries). It does retain settings between AA battery changes, however. I guess you could check if (e.g.) a custom function setting is preserved in the faulty camera when the AAs are taken out and replaced.

I have a couple of F100's living a life of quiet, battery-less vacation. So I got out an ohmmeter and tested them (there are two clearly visible terminals when the battery holder is out. You need fairly long thin probes to hit them). When sitting with no residual power, turned off, an F100 draws no discernible current at the 20 megohm setting. When turned on, they draw a fluctuating amount in the single digit megohms, which then persists after turning off. But if you short or load the terminals briefly, the reading goes back to an open circuit. I presume that this means any retention of settings and readings comes from a capacitor, or in the case of custom settings, perhaps from a PROM chip. That's of limited help here, but it does mean that if you have an ohmmeter, you can test the camera's power draw whan off and on, and eliminate the battery and holder in diagnosis.