Hmmm...
https://www.snopes.com/fact-check/radioactive-diamond-batteries-real-thing/
...The actual amount of carbon-14 in each battery has yet to be decided but one battery, containing 1g of carbon-14, would deliver 15 Joules per day. This is less than an AA battery. Standard alkaline AA batteries are designed for short timeframe discharge: one battery weighing about 20g has an energy storage rating of 700J/g. If operated continuously, this would run out in 24 hours.
...Using carbon-14 the battery would take 5,730 years to reach 50 per cent power, which is about as long as human civilization has existed. However, it is unlikely that the diamond battery will provide direct power to an attached device. More likely is that it will be associated with a capacitor that will be ‘trickle charged’ by the battery and then discharge at set intervals, to power devices at set intervals or to continually power low draw devices.
Excellent post.
I note that proponents carefully avoid any discussion of actual current delivery capacity. However, even keeping everything in Joules, the problem is obvious.
If an AA “diamond battery” is going to contain 1 gram of carbon-14, delivering 15J / day, that’s just not going to cut it for most applications. Running the number provided for an alkaline AA cell, 20 grams @ 700J/g gives you 14,000 Joules of energy storage.
As a “practical” application, I consider a small, not particularly bright AA LED flashlight I keep handy. I’ve never timed it precisely, but I believe it will provide useful light for about a day, if powered by a fresh alkaline AA battery. This is right in the alkaline battery’s wheelhouse, efficiency-wise. Average light output over the 24 hours is probably 5 lumens at best. The flashlight used 14,000 Joules in that day to do it.
15 Joules per day for the diamond battery is going to be kinda dim...
The “out”, as you suggest, is to use the diamond battery to charge a capacitor, which can discharge at a high rate. So... one adds the capacitor, and assuming the 1g carbon-14 element still fits in, in full, what one has is, in effect, a self-charging battery. However, at 15J/day, it takes 933 days to fully charge to run my flashlight for a day. That’s neglecting charge losses, self discharge of the capacitor, etc.
This leaves, as you stated, “interval” usage — something that pops once a day at moderate current, for example, and low drain uses. How low?
As a very rough comparison, that 14,000 Joule alkaline cell AA battery mentioned earlier likely has a capacity of 2500 mAh if used ideally. That relationship applied to the diamond battery gives us about 2.68 mAh available per day, essentially until something else breaks down. If used continuously, that’s about 0.110 mA.