Unless a permanent repair can be done then insulation tape won't last with rain and cold. As asked some pics please.
Depending on the damage sugru, epoxy resin or even fine grp matting/resin could be used to repair to make water tight/safe.
I've twice repaired badly damaged battery cases using Duct Tape with lifelong success. One silver case I repaired with black tape I later corrcete with silver duct tape for a good match.
Also depends on how it split, if dropped hard enough to damage the case what condition are the cells within.
Lithium cells can behave badly when angered.