Q:

Can a bad lens contact cause false battery warnings?

I had a major problem with my Nikon D80 lately, in that after taking 1-2 pictures or just leaving it on for around half a minute, it would give me a battery warning before turning itself off. This happened with several battery packs, all originals, fully charged, and persisted after cleaning battery contacts. When turning the camera off and back on, it would display full battery charge again, only for the problem to return straight away.
Concluding that it was a defect with the camera itself, I replaced the lens with the cheaper kit one, in preparation for sending the camera in for repairs. Then I noticed that the problem went away. Now, I can't reproduce the issue even if I put the other lens back on.
While I understand that a bad contact between the camera body and the lens can cause a variety of issues, this particular symptom seems strange to me. Is it possible for a bad lens contact to cause the camera to falsely think its battery is drained? Or can it actually cause a drop in voltage like that? I want to be sure that it's actually physically/electrically possible to have been the cause, because if it's just a coincidence that the problem went away after changing the lens, it's sure to return next time I'm out trying to shoot.

A:

While I understand that a bad contact between the camera body and the lens can cause a variety of issues, ... is it possible for a bad lens contact to cause the camera to falsely think its battery is drained? 

Yes, maybe.

I'm an electrical engineer with substantial low level software involvement. Plus I have professional experience of analysis of fault histories (in another but relted context). I do not "like" the following answer BUT it is a reasonable one.
Software related problems can have both obscure causes and obscure and sometimes unrelated cures. Sometimes an apparently unrelated action can fix a problem that it was not the cause of. Lens demounting/mounting has fixed a number of problems for me - in one case a consistent but very occasional  problem was  consistently fixed by lens demount/mount action. 
In the case of your camera, it is entirely feasible that the lens change either fixed an unrelated problem , or that the lens contacts did cause the problem. However, there is no certainty that this is true and the problem may have been caused by another problem and may reoccur. Unless the problem is one which is common and which the repair shop has gained experience of, "waiting for next time" may be all that can be done. 
It's  possible that there is some other measurable indication of a problem that  a repairer may uncover, but my experience of fault repair (as a one time professional analyst of fault histories in another context) suggests it is more likely that a workshop return will fail to find even a real but now latent problem.

Some years ago I had major problems with a Minolta DSLR that seemed to have no relationship whatsover to the lens system. I was in Singapore at the time and dropped in on the ever helpful Steven  Lee at Camera Hospital. He said that the lens electrical contacts were a prime suspect. He said that many obscure problems were caused by poor lens contact problems. Even though I found this extremely unlikely in the case in question, a little "playing" showed that ensuring the contacts were OK fixed the problem and it did not reoccur.
On A Sony A700 with a SAL18250 lens I found that very occasionally the image would suddenly assume a strong Magenta hue in the saved photos. Turning camera power off and on again did not fix the problem. In that case disengaging the lens lock, turning the lens a part turn and then reversing it till it locked would cure the Magenta hue problem. This occurred only occasionally, typically months apart, but the 'cure" always worked instantly.
The key point is that in both cases the problem MAY have been caused by a contact problem and remedied by fixing the problem, BUT it is possible that the problem was caused by happenstance or by a memory bit being randomly flipped by an alpha particle hit or by Murphy at work and that the lens unlock-lock sequence caused a software action that updated the erroneous bit quite coincidentally. ie in the latter case the lens mount disconnect-connect sequence may have been the cure but not the cause.

