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For anyone who still has devices with old AA, AAA, C, D, or 9V type batteries in it I highly recommend you move over to the USB chargable Li-ion type of the same format.
Most of those devices dont work with traditional rechargable batteries like NiMH because the voltage is a bit lower. Even if they do work they tend to last only a short period of time because as they discharge the voltage drops even further. So your device will often die even with 70% of charge still in those batteries.
With the newer USB rechargeable Li-ion type batteries of the same form factor, however, you have a drop-in replacement that doesnt have those issues. They basically are a LI-ion battery with a built in charger but more importantly with a DC-Dc converter to keep the voltage fixed at the desired voltage (1.5V or 9V) for the entire life of the battery. So they work in any device that they can fit in and lasts a long time as they deliver 100% of their power before cutting out (at which point it drops from 1.5V directly to about 0V).
The only downside is if your device reports a battery percentage then it will report 100% battery right up until it hits 0.
Anyway I replaced all my devices with batteries like this and they last longer than regular batteries in some cases (especially with 9V)... so I am sold!
This is Mur 
@freemo
But how will I extract graphite then?
@mur2501 Use pencils, it wont be caked in chemicals that way either. The easiest way I found to get them out of pencils is to expose the graphite on both ends then hook a voltage onto it. Crank it up until the pencil starts smoking, leave it like that for a minute or two, turn it off, let it cool down then the graphite will slide right out.
+bonifartius 𒂼𒄄
@freemo just get the refills for mechanical pencils? not as spectacular though :D
i'll try out those batteries, i have a cheap wildlife camera which requires 8 × AA..
@bonifartius mechanical pencils have very thin graphite. Not very useful for most applications.
Though I will say electrically burning thin graphite from mechanical pencis is one of the more fun things to do. They glow insanely bright, dont catch fire, and just evaporate into CO2. So makes for a fun show :)
@freemo, there actually are, and you do need to sharpen them, but the sound is much nicer and you can eat the byproduct (well technically you can also eat wood but it tastes terrible). They’re more useful for artistic drawing I think.
Cc: @bonifartius
@bonifartius I have never seen a mechanical pencil with a particularly thick lead on it. In fact I dont think that would work too well since it wouldn't create a sharp point without sharpening, which you cant do for a mech pencil.