Listed below are the results of forum members attempts at
building a low cost external battery pack for the Sharp Z-5000.
USE AT YOUR OWN RISK THIS WILL VOID YOUR WARRANTY

Sharp Z-5000 Power Specifications:
     Internal - 3 volts, .5 watts 
     AC Adapter - 8.5 volts, 350ma center pin negative
     Sharp External Battery Pack - 7.5 volts, 350ma  center pin negitive

Optional Battery Packs as reported by forum members:

Pack 1 as used by Mike Ziegler, 76506,2353
     Radio Shack 9.6volt NiCad pack for race cars cat# 23-229. 
     Radio Shack 9.6volt battery charger for 23-229 cat# 23-240A
     Sharp EA-23E adapter. Clip the plug from the adapter for the battery
pack.
     Center Pin MUST be negative.
     Radio Shack even has an extension cord with male plug on one end and
female on the
     other for a very professional looking rig.
     Powered the Zaurus for several days and sent 6-2 page faxes.

Pack 2 as used by Bo Lorentzen 74673,2401
     Radio Shack  generic 6AA  battery case with 9v snap on one end.
     Sharp EA-23E adapter. Clip the plug from the adapter for use with new
battery pack.
     Soder plug to connecter and zip tie to plastic case.
     Center Pin MUST be negative.
     Powers Hayes Optima 144 pcmcia modem online for over 2 hours.

Pack 3 as used by Sebastian F. Gaglio 70531,2405
     Radio Shack 7.2volt battery
     Radio Shack 7.2volt charger 100ma
     5.5x2.1 Coax male for battery pack
     5.5x2.1 Coax Female for battery charger.
     When the 7.2v battery pack is fully charged it reads 8.5volts, the same
as the Sharp 
     AC adapter. It takes about 14 hours to recharge. 
     Center Pin MUST be negative.
     Powers Megahertz model XJ2144 pcmcia modem just fine.

The Sharp Z-5000 will accept 7.2v - 9.6v DC as report by these users with no
ill effects.

If you are using a plug other than a cannibalized one from the Sharp EA-23A
adapter take your Zaurus with you to test the fit of plugs at a Radio Shack
or a local Pro Electrionics store. 

Good Luck.