Is there a splice kit that would allow me to tap the positive and negative connection and add a pack of 5 different packs I put in my trunk in a big plastic box with some foam pads?
While there are a few people who can safely handle 300+ DC volts, with high amperage to boot, most people can't, and making such a kit easy to acquire would likely result in a few electrocutions.
This is how I tap it on 2011-2012 original packs, easiest pack to do.
Wires are connected directly to a contactor unit(didn't have a photo, sorry).
On 2013+ cars(24, 30, 40) where is a modifications of the pack required to do so with a current sensor relocation, new wire on a place of the current sensor and wires extension for a current sensor.