His review conclusion didn’t seem overly optimistic.
“Conclusion
_The sleeve is not really a product to save a lot of batteries with, there are probably a few products where it will increase the runtime for batteries, if it can fit in them (Many devices has a fairly tight fit on batteries).
With some devices there is also a risk that either the ripple or the switcher noise will prevent them from working correctly.
Due to the nearly constant output voltage until the battery is empty, battery meters will not really work when using this device.
To find devices where it might be useful, look for devices that have very short runtime with NiMH batteries and considerable longer with alkaline. The sleeve might be more useful with NiMH batteries than with alkaline. The question is how hard the 0.6V minimum will affect lifetime of NiMH.
As a general device to extend battery life it is not very useful, but in a very few situations it might be a useable solution._”
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Then I saw this thread……
Batteroo
It’s an interesting idea, but the real benefits don’t seem as great as advertised and I don’t want to risk damage to my rechargeables.