We all know who Iron Man is.
Hollywood makes a nice job to make him look like a genious in electronic.
However, there is a scene where his suit charges it's batteries to 475%.
There is another question, on another website, adressing one part of this issue.
You can read it on Can Iron Man recharge his suit from lightning?.
What I'm asking here is if it is possible to charge a battery (no sci-fi stuff, please), with current technoligy, to over 100% of it's charge without exploding?
Well if you say 100% is the capacity of the battery specified by the manufacturer, then yes nearly all batteries are charged beyond 100%, as the manufacturer will indicate the minimum capacity, so they are not made liable for any failures concerning too little capacity.
But that's in the range of maybe a few percent and not a massive 375% or something like that.
The reaction to overcharging the battery is very dependent on the chemistry involved. Some will tend to explode (lithium ion and lithium polymer), others will just waste the additional charging current to heat.
The point made by PlasmaHH in the comment is actually a quite good one. If a battery could hold significantly more charge as advertised, the manufacturer would be quite dumb. Now you could argue, that a lot of ICs will also run at much higher speeds than advertised. But on closer inspection, not all ICs are able to, and that's why manufacturers turn the speed down to a level where every chip runs - it increases the yield and thus you can make more money. Batteries seem to behave more predictable for manufacturing.
Maybe a capacitor can handle more voltage and so store more energy than advertised. As the energy stored on a capacitor increases with the square of the voltage, you would need to double the voltage to store four times the energy.
That doesn't sound too bad actually - you might find some capacitors which are able to handle double the voltage specified as they are tested quite hard. But then the energy stored on capacitors is quite low compared to batteries. (There are massive capacitors, but you wouldn't want to carry one around)
There are plenty of battery chemistry options which can be left on a charger without damage - but that doesn't lead to higher charge levels!
Fundamentally a battery works by adding and removing electrons from atoms in solution. This sets an absolute physical upper limit on how much energy it can hold, in the same way that you can't put more than 1L of fluid in a 1L bottle: once you've run out of atoms to change the charge state of, there is nowhere to put extra charge.
NiMH batteries will take the excess charge current and liberate flammable hydrogen gas (which is vented to prevent the cell from exploding) plus heat, permanently reducing the capacity of the cell (damaging it). In extreme cases (like the example), thermal runaway takes place which doesn't just damage the battery, it destroys it on the spot in a geyser of electrolyte steam and liberated hydrogen. Lithium cells can turn into pyrotechnics, presumably incinerating the unfortunate Mr. Stark.
While it's possible that you might be able to get a small amount of extra capacity at the risk of damaging a battery in general, if 475% was possible they'd be using it.
As others have explained, what you call "100% charge" is definitely not fully charged. Battery people don't necessarily figure out what 100% charge really means because the battery usually explodes when you get there.
I'm most familiar with Li-ion batteries, so here's a quick "oh my god" situation:
The Li-ion batteries I work with have two flat electrodes rolled up with a separator in between so that the electrodes don't short together. If you hold a battery at high voltages and temperatures for a while, something similar to tin whiskers can form on the electrodes, causing a short and generating a lot of heat. The battery will probably catch on fire (and lithium fires are particularly nasty).
Note that charging batteries to higher voltages will also cause them to die in fewer cycles without a whole lot in return. Most of the capacity of a battery is in the lower (regular) voltage ranges, so adding an extra 100 mV of charge won't make your battery last as long on one charge as you think.
