Silver-Zinc batteries are said to be safer and more environmentally safe than li-ion batteries but unfortunately your laptop will need to be specifically designed to handle these new batteries so you won't be able to upgrade existing notebooks.
ZPower has been in the news before, with previous claims that the first Silver-Zinc batteries would come to the market in summer of 2008. It seems that estimate has been pushed back to 2009 with new promises from the company that battery option will be rolled out "in a major notebook computer in 2009."
Aside from increased run-time, ZPower also claims that Silver-Zinc is safer and more environmentally safe. Silver-Zinc is said to be far more chemically stable than Lithium Ion which has had widely publicized problems with overheating and igniting. As well, 95% of battery elements are said to be recyclable with financial discounts offered to customers when they trade in their old Silver-Zinc batteries.
Existing laptop owners will be unable to take advantage of Silver-Zinc batteries when they arrive on the market. New laptops will have to be specially designed to handle the new batteries but can be "dual chemistry enabled" allowing them to use both Lithium Ion and Silver Zinc. Silver Zinc is expected to be initially offered as a premium upgrade option.