After a few days iFixit performed a teardown on the Apple Watch Series 5 44mm, they conducted another teardown of the smaller 40mm Apple Watch. The smaller size Apple Watch has more significance in its components than their larger size models.

For example, the battery is encased in a rigid, light aluminum metal plate instead of crinkly, gleaming foil. This is the first time Apple has covered the batteries with a sturdier metal plating, according to iFixit in the light of the Apple Watch battery patent. The company also noted that it is a “more space-efficient method for sealing up batteries.” Apple is managing to compress the battery down to allow more battery capacity while retaining a slim, compact shape in smaller Apple Watch models. In contrast, foil batteries leave a much larger, ballooned seal than the aluminum encased batteries.

iFixit explains the extra protection of the smaller, 40mm Apple Watch Series 5’s battery, which depicts the aluminum metal shielding on top of the battery’s cells. They stated, “Additionally, the metal casing makes the battery physically stronger. This is fantastic for repair purposes since it’s all too easy to puncture a lithium-ion battery during repairs. The outer metal shell should allow device owners to pry out the battery without risking damage to the internals, reducing the associated fire hazard.” In this way, Apple is trying to lessen the likelihood of battery explosion incidents during repairs and usage by making a protective, thicker metal membrane on the outer layers of the battery. The company is also responding to the June MacBook battery explosion recall by fastening all of its batteries with screws instead of messy, sticky glue. One exception Apple hasn’t done to the new Apple Watch Series 5 battery is the lack of these tiny screws to keep it in the chassis, due to the fact that it can compromise the size of the battery.

Although Apple never used screws to keep batteries secured inside iPhones and Apple Watches, the metal shielding in the Series 5 Apple Watch 40mm adds in the slimness of the long, 18-hour battery life while retaining its same size. It prevents the risk of battery fires and accidental punctures during battery replacements by using it as a rigid, lightweight aluminum membrane. Apple may start improving batteries in their products in the future, once new products roll out in the coming months.