That's great
The voltage stabilizer improves voltage supply which in turn means no loss in battery life or performance. It provides a stable supply to all the electronic components of the car including the ECU, resulting in slightly smoother performance and efficiency. Recommended for cars with accessories that require high power from the battery.
You don't need to change the holder, and the wiring was a DIY
You'll find quite a lot wiring diagrams if you search for this on google