[hangonhn]

But why not go nuclear? Not a full on nuclear reactor but one of those nuclear RTG batteries. The half life might be low but could you not keep doubling the amount until you reach the requisite years? Basically take the amount of Pu you need to power the device, and double it 20 times (half life of Pu-238 (87 years) * 2 ^ 20 >= 55 million years). This way the entire unit is self contained and you can encase it in whatever super durable material you can think of -- artificial diamond/sapphire.

[yellowapple]

Hell, ain't Africa home to some giant natural fission reactor? Reignite that thing and there's your power source.

[scrumper]

Because the power source isn't the problem. It's the mechanicals in the speaker.