In addition to all of my other troubles with connectors, the heatshrink that wraps my MagicShine battery is starting to split.

For now, I've temporarily taped over the ends of the battery with self amalgamating tape, but this certainly not a good enough fix.

I thought about wrapping it in rubber (from an old inner tube), but doing this will not allow it to fit in the little velcro bag.

I could try to find more heat shrink (in that large a size it will not be simple).

Anybody have any suggestions or experience?

I've got one of the all-battery packs coming which has 8 cells instead of 4, so I'm planning on just moving to a bigger bag anyway and losing the included bag.

I will probably try to find a waterproof handlebar bag, or to make the bag I use waterproof, perhaps just with a ziplock.

I just noticed this morning that the insulation on my MS pack's connector has split and the wires inside have become visible. This is the case even though I've been very careful to only grasp the connectors when separating them. Apparently just the act of twisting the two connectors (which is absolutely necessary to separate them by hand) is enough to damage the insulation.

Try liquid tape. It really works well. I use to use it when I built Halogen light systems before switching to Fenix lights.
https://www.idealtruevalue.com/servlet/the-146314/Detail

The liquid tape looks great. I've painted it the battery with it, and we'll see how it comes out in the morning.

I rigged mine inside a water bottle