Blazer 97 battery drainage

I have a strange problem with one 97 blazer w AT transmission. It started few days ago while driving - the battery indicator showed up and the voltage gauge started to drop down and after a while the transmission was not working. First I thought the battery was gone but I've checked it and it is OK. Now if I turn the key to start the engine sometimes I hear some clicking noises and the rear door lock is making noises too. When I let the car sit for a while I can start the ignition, but sometimes the gauges are dead or the voltage gauge is dropping down. Last time I 've just turned the key to ON position (engine was not running) and as soon as I hit the brake the voltage gauge was going down. I think it must be some electrical problem (short circuit or so). Have any clues?

First, I would recheck the battery condition and take a close look at the cables for signs of corrosion.
Also check the positive feed to the underhood fuse box.
Have your battery checked with a digital battery tester (midtronics works well)

With your comment about the transmission not working, has the SES light come on?
The transmission shift control circuits are powered by the ignition switch (which has been known to cause some problems)
But check the battery and charging system first...low voltage problems play hell with the computer

Don't forget to have your alternator checked. Mine did the same thing, I had the alternator checked, it tested GOOD, but after further investigation, I just went ahead and replaced the alternator and that was the problem.

There is a TSB out for 98 blazer so i don't know if its the same for yours, but the red wire that goes to the battery indicator and voltage guage shorts out against the heater hose bracket. Once this happens the battery light will come on and the alternator will not charge, but the alternator itself is still good you just have to fix that wire. The transmission is electronically controlled so if the battery is dying it won't work right. When this happened to me the battery guage would go down and the car would only idle as soon as i hit the gas it would bog down because there wasn't enough power to power the fuel system.