"I did read that some old motherboards wont turn on without a working battery?"

Yes, happens with old 68k Mac all the time. They need a push on the reset buttons, too. NVRAM, Parameter RAM etc.

On old ATs, the clock chip contains the BIOS parameters. They're stored in the unused parts of the RTC's (Real Time Clock's) SRAM.
So if the on-board clock has no power, that SRAM is dead.

And some BIOSes simply won't boot with an inaccessible SRAM.
These BIOSes require the SRAM to hold the configuration data, even if the SRAM was empty during power up.
If it was empty, I assume, a routine would stupidly upload default settings and then the BIOS or CMOS Utility would read them back as if everything was normal.

Other BIOSes just load the default parameters into RAM from within their BIOS ROM chip.
Those may POST and report an RTC failure.

Thanks that was some pretty good info, didnt work on that mobo but it might have some other faults too. But good info thanks!

Hi, still troubleshooting this mobo on and off. Iam not an electronics pro so it takes time 😀

But i noticed that -12 in the isa slot is actually giving +0.7. There was a transistor 3904 or 06 dead that drives the battery circuit. One leg just stayed in the mobo. Changed those, round part towards the shorter edge of the mobo.

If i put the isa diagnostics card in the upper isa slot, it kinda dies and the psu shuts off or the card. The leds just fade out. But in the lower section it stayes on but no post, every led is on.

I know that shorted caps can drive the -12 mad but any suggestions? I know there can be traces under the isa slot that are broken, it is a varta mobo afterall with all the juices 😀