I'm pretty sure I saw an answered question about what Vader's chest buttons do on this site before, but failing to find them again, I found the same answer on Quora.
In the battle against Batman, he pressed two buttons: The bottom red one, then one of the three white ones. Although the video is fanmade, it appears enough attention to detail was given to ensure consistency with canon button functionality:
The rightmost switch, located at the bottom, acted as a system reset while the rest of the four switches located at the bottom were programming touch plates.
So basically, Vader rebooted his suit.
As we have discussed in the comments, Wikipedia defines EMP's effects:
EMP interference is generally disruptive or damaging to electronic equipment, and at higher energy levels a powerful EMP event such as a lightning strike can damage physical objects such as buildings and aircraft structures.
Quoting your own comment:
If the intensity isn't high enough to fry wires, it can at least fry capacitors or other equipments (If the device went down, there must be a reason). If there was a self-repairing fuse, it shouldn't have taken long time to repair. Such fuses get back in action within seconds.
This branch of engineering isn't my area of study, but assuming you are correct, there's a few points to take note of that may be relevant to the suit's capabilities:
- Palpatine may be deliberately restricting his apprentice with a suit containing obsolete tech and poor design, but he wasn't ready to leave him for dead (yet). The suit restricts Vader a whole deal when it comes to comfort and freedom of movement, so he will always be ever so slightly distracted, but it is extremely well-built where it matters - he is well-armoured even against lightsabers, and he is immune to many environmental effects, including subzero temperatures and the vacuum of space. Basically, it's not comfortable but it's very resilient. It may be vulnerable to electricity, but it may yet be able to recover or survive that.
- During the Clone Wars, the GAR made extensive use of ion grenades to disable CIS troops like droidekas for easy termination. It would make sense that Palpatine would want Vader protected from similar tactics during the long years of maintaining an Empire.
- The belt does have a spare power cell.
On his belt, Vader wore two small system function boxes: the one on his right featured a temperature regulation system and the one on his left contained a respiratory sensor matrix. The center buckle featured an audio enhancement unit built into the electromagnetic clasp of the system status belt. Also included in the belt buckle was an audio-enhancement unit, small tool kit, spare energy cell, and backup comlink.
This may not exactly match the features implied in the battle with Batman, but we know that's fanmade. As for in-universe, I won't be surprised if the spare power cell is protected from EMP/ion attacks and is internally configured to kick in after such an attack, whether automatically or manually like Vader did in the video. Remember, Palpatine wants him alive still.
If you notice, there's also a toolkit on the belt. That would allow Vader to, technically, conduct "self-repair" in general.
Edit: The only known modification Vader made was to reduce his vulnerability to Force Lightning, insulating his components. He can't remove the vulnerability completely, but he is at least able to greatly increase his tolerance for it, both in scale and intensity. So his armour is possibly more resistant to EMP than we think.