PowerBook 540c PRAM battery problem

[MikeatOSX]

Hi there,
I own 3 PowerBook 540c and I'm very happy with them. One has a SCSI2CF and another has a SCSI2SD built in, everything works but all 3 have a little problem: after a few minutes without power supply, my PRAM settings disappear. Date & time and energy store are deleted.
Date & time I can restore with Vremya or SetDate, but the PowerBook also wants to put the SCSI2SD to sleep after a short time loose it's own SCSI connection for a 3 or 4 seconds. 
So I also have to adjust the PowerBook control panel each time. 
Now I've disassembled a PB540c to add a new PRAM battery, but the old batteries show 5.62 volts! 
The new ones are 2x3 = 6 volts.
Is the old battery still ok and there's a different reason?
Can anyone give me a hint?

 

[IlikeTech]

I would guess that 5.62 volts will fall to 0 with even a tiny load...

 

[MikeatOSX]

I'll see it soon: I have replaced the PRAM batteries and I'm reassembling the PowerBook now. 

 

[MikeatOSX]

No difference with the new batteries. As I don't have a working main battery for my PB 540c, I let it sit provided with the power supply. Maybe after some hours I notice a result. 

 

[IlikeTech]

I think I heard that PowerBooks require a good main battery to charge before charging PRAM batteries.

 

[MikeatOSX]

Maybe PB 500 series. 

I tried this with several PowerBooks 5300, as all of their main batteries leaked and are dead. 

All PRAM batteries of them are charged by the power supply board, when they are sitting for hours connected to the power supply. 

 

[MikeatOSX]

Two of these batteries fit, must be soldered to the old cable. 

 

[MikeatOSX]

After hours of connected to the power supply the PowerBook 540c now holds all it's PRAM settings, when disconnected for some time.  [8D]