[gatagato]

The most common name is AA, also called Pencil-sized, mignon, Type 316... it has even more common names but the list of IEC names is

LR03 (alkaline)
R03 (carbon–zinc)
FR03 (Li–FeS2)
HR03 (NiMH)
KR03 (NiCd)
ZR03 (NiOOH)

Low voltage batteries contain high amount of energy, but what really caused this mess is the fact that he closed his mouth. When you short-circuit one (but he was handling 3 ones, in series) in open space apparently nothing happens: but if you twist the wire with your teeth and close your mouth, the small part of wire that gets vaporized in case of short-circuit will emit so much energy that won't be able to dissipate: in a closed cavity (his closed mouth) this resulted in a blast, so not the batteries but his mouth, exploded, literally, like a strong leak of gas into a closed room ignites even just from a extremely small spark, turning the room into a bomb.
Never try this at home, ffs!
There's a paper about this case
(© National Journal of Maxillofacial Surgery)
Blast injury face: An exemplified review of management (2013)

[wee_yumi]

What's a pencil battery? And he didn't die?

[vagabond]

That poor child

[kustom80]

Jesus wept, poor kid. One trivial thing has destroyed his life for good.

[MrCorpse]

Shame it survived, all we can hope now is that with such a disfigured face it is unable to pass on these faulty genes.

[hardy-harr]

well i bet he learnt his lesson

[kellyhound]

holy crap

[Kelseecat65]

Originally Posted by XybertroniX ↗

we call them in easier terms. "AAA" or "AA" or "C" or "D" or 9v square batteries

Yep!! That's makes much more sense to me! LOL

[Aurora_623]

Originally Posted by gatagato ↗

but if you twist the wire with your teeth and close your mouth, the small part of wire that gets vaporized in case of short-circuit will emit so much energy that won't be able to dissipate:

No, those batteries have short-circuit currents <<10A.
For the thing you describe, you need an impulse of many 1000Amps.
Not even a 12V plumbum accumulator (as used in cars) could do that.

You need:

• high voltage to get the current through the wire - rectified 3 phase ac (~560V) fits well.
• a storage for lots of energy with low serial ressistance: Electrolyte capacitors, many of them and paralleled.
• a "switch", able to turn on extremely fast and to conduct such high currents: An ultra-low rdson-FET or a big thyristor...

[Oswald2001]

Looks more like a blasting cap injury.