ANother ebay thing... I think it might have been mentioned before.
There is an ebay store selling a lithium-polymery 1700mah battery for about $10 usd. If it wouldn't cause problems for the Z, this might be a cheap handy spare. I thought I'd mention it becuase it seems a little to good to be true. For $10 I'm ok with relatively short life, but not ok with any risk to the Z--thought it might be a good idea to ask around.
Before anyone recommends either a sharp battery, or one from lion batteries--I plan to pick up one of those soon anyway.