Silver-zinc batteries.

[10.5]

Found this old article:

http://www.gizmag.com/go/7743/

Silver-zinc, now in rechargable form.

Currently offers 30% more energy density than li-ion, but being made of silver, are expensive.

They're safer, and 95% recycleable

[PatQ562]

Claims seem to be a little hard to pin down. Wikipedia shows 130wH/kg in one paragraph, Zpower claims 200Wh/kg further down, and claimed "30% better" than lithium 3 years ago which would only be at par with today's lithium. They also focus on energy per cubic inch ie "the same size battery will run longer" which ignores the weight factor (lithium is light, silver is heavy). Historically, zinc based systems have suffered from unreliable recharging due to whisker growth. I tried a batch of Evercel's Nickel-Zinc batteries several years ago, which promised twice the energy per pound as lead acid, which I more-or-less confirmed when new, but they leaked, gassed, and didn't work well the following year. Zpower was proud to get 200 recharges in 2007, which is good for silver-zinc, but far short of the 1000's we want for lifetime service. And of course, silver is expensive and limited in supply.

Pat Q