My iBook G4 do not stay with power.Not more than 90 minutes. Is this normal?

You probably need a new battery but that machine should only get about 3-4hours with a great battery.

There are several models of iBook G4. The following sequence applies to the "14-inch Early 2004."
Remove all peripheral cables. Remove the battery. Reset the power manager by pressing the key combination Control-Option-Shift-
power. Then plug the iBook into AC power and attempt to start it with the power key.
If this procedure does not being it back, invasive diagnostics are required, in which case you should being it to an Apple-Certified tech for repair.

hello , if there has been any 3rd party memory installed remove it and attempt a PRAM reset again , as well you may try a PMU reset as it appears your issue is power related.

Use the free App called iStat Pro to monitor ALL temperatures. Give your Mac some air (literally)
There is a big difference between CPU Temp and, for example Enclosure.
You also may have a very high CPU usage for a while.
Check if your fans are running high I.E 6000 Rpm
@How2Mac

Open System Preferences:
Click on the Lightbulb Icon entitled "Energy Saver"

Adjust the preferences for each of the two options:
Put the computer to sleep when it is inactive for:
1min 15min 1hr 3hrs Never
Put the display to sleep when it is inactive for:
1min 15min 1hr 3hrs Never

Set these for Power Adaptor and Battery separately.

Try resetting the PRAM by turning on the iBook then holding option + command + P + R and wait till u hear another chime. If it still freezes, it may indicate an application may be causing it to lock up hold shift after you hear the chime to boot OS X into safe boot.

This is nearly impossible to diagnose via the Web. It sounds like the logic board is at fault, but not necessarily.

http://coreyarnold.org/ibook/?p=20

On an Apple system, this is an indication that it thinks there is little or no battery left and goes to sleep to protect data loss. Your battery might be going bad (showing a full charge, but lasting for only a few minutes) or there may be a problem with your power supply.