Global quest to improve performance drives battery R&D toward ever-higher energy densities. High gravimetric energy density rewards battery users with lighter portable or mobile power sources and longer operating times between recharges. Product safety & reliability could be the hidden costs --- higher energy density is a two-edged sword that cuts both ways. Internal electrical shorts, hot sparks, and catastrophic electric arcs are reducing durability and causing thermal runaways, fires, and even explosions in Lithium-ion batteries. Ultralow energy neutron reactions (LENRs) may be causing some of these extreme events; engineering for LENR effects could potentially help improve future battery safety and durability.