The specs appear fair (better than stock) but with 10.5.8 it still will seem slower
than Tiger 10.4.11; enough RAM helps, yet will prefer to use swap space as VM
from the hard drive in addition to chip RAM. You may consider a PMU reset, yet
that won't fix a depleted, worn, and out-dated battery. A second power adapter
is often a recommended idea as it may help in troubleshooting power issues.
•PowerPC-Based Mac notebooks: Identifying the right power adapter and power cord--US - Apple Support
The battery should be replaced. I see (but have not bought) a quality third-party
replacement appears at OWC laptops page for under $90. usually. Note which
display size you have, since battery number will matter, for power requirement.
Examples of a suitable quality replacement with guaranty for portables with a
user-replaceable battery are in second link directly below:
http://eshop.macsales.com/shop/powerbook-ibook-macbook/ - general portable
http://eshop.macsales.com/shop/Apple/Laptop/Batteries - batteries/general
An iBook with 14-inch display uses a different battery number than the 12-inch.
You may be able to locate a good condition original/official Apple power adapter
for your iBook; or you could use a new generic power adapter with similar plug
from a company such as OWC, among others. These do not have the colored
light in the power plug to indicate charge status, however.
You may need to see if a reset of the Power Management Unit (PMU) helps,
but it will not restore a dated and failed battery; their life is up to two years.
•Resetting PowerBook and iBook Power Management Unit (PMU) - Apple Support
A 'legacy SSD' in ATA/IDE build, for use in older computers is available from OWC
and though it is a pain to open these, you could speed it up. But then what? Maybe
set it up to boot from some other OS such as linux or other custom build for PPC.
A failed wireless component may be the dual-purpose wi-fi circuit that is attached
to the logic board and is not (in last iBook models) a user-removable part. See that
item in the iFixit.com repair guide for late model iBook G4, as it can be replaced.
Companies such as powerbookmedic & wegenermedia have options for old 'Books.
Anyway, hopefully this helps somewhat...
Good luck & happy computing! 🙂