While sparked, PCLN creates DEUT. It's cooled to -273.15 (absolute zero) so that it can be compressed into an extremely tiny space. It's hard to get an exact number, but based on the number of DEUT particles that fit in the tank, I've estimated that it's around 100,000 or so.
There is a wall below that part, and if it's turned off, the DEUT goes into a second tank. It's heated to around 3000 degrees, which makes it expand to more than its original size. To make sure it's fully heated, it's slowed down by portals and DMND.
Finally, there is a second wall that can either keep the DEUT in the battery, or destroy it to create electricity.
You can also charge one tank while emptying the other by closing the first wall after some DEUT passes through it.
It takes about 10 seconds for a particle of DEUT to travel through it, so it works best when you charge it a few seconds before you want to take sparks out.