Over a year ago I noticed that the track pad on the Apple laptop I bought in 2013 wouldn't click anymore. Since I almost always use a usb mouse I set the track pad preferences to tap-to-click and left it that way. But as more time went by I also noticed that the laptop no longer sat flat on the table. A quick internet search turned up failed track pads as usually being caused by swelling batteries. A warped shell would also happen if the battery swelled up.
Step 1: Battery Cheap, Laptop NOT
A replacement battery is about $30 on eBay.The laptop cost well over $1k. The swelling would eventually lead to a cracked main board or a fire. This was a no-brainer. Even though the battery still held 80% of design charge it needed to be replaced. I have had this laptop open before to add ram, so I knew it wasn't hard to do and did not justify paying Apple $180 to swap out the battery for me. After taking the screws off the bottom shell I could see it wasn't safe to try and force the shell back together with the old battery inside, so I left the shell partially unscrewed.
Step 2: The Screws Are #0 Phlllips
A $1 screwdriver set from Dollar Tree was all I needed to remove the bottom screws. The battery connector lifts straight up with just fingernail pressure, no tools were needed. I dusted off the inside with a soft, clean paint brush while i had the back off. If you unplug the battery the laptop clock reverts to the year 2000. When you plug the battery back in and plug in the charger the laptop turns on without being prompted. You can either manually open date and time prefs and set the clock or wait until the laptop finds the internet and calls home to Apple's time server. As long as the date/time prefs are unlocked that is enough to get the time correct again. If you don't correct the time or allow it to be corrected you cannot surf https sites because the ssl certificates have start and expire dates and they will be out of range of the system clock.
There are 2 screws holding the battery down. Those have a Y head. I didn't have a tri-tip screwdriver to use, but a small straight blade was enough to unscrew them. Sometimes the battery seller will include a triblade screwdriver with the new battery. My seller didn't.
Step 3: Checking the Fit and Trackpad Function
After removing the old battery I flipped the laptop over and confirmed it sat flat the the track pad clicked. The I installed the new battery and repeated the checks. The new battery fits and the trackpad now works correctly.
Step 4: "New" Battery Really Isn't
Note the manufacture date of the battery was 292 days before I installed it. Not exactly fresh, but load cycles is 1, so this battery hasn't been used before. It came with a 38% charge, ground transportation only, because this is a lithium battery. The last pic is the inside of the older battery. The cells feel like they are full of air, but they are actually full of H2 and O2 gas from charging, so I am not going to break the seal. Besides I wouldn't want the cells leaking on anything, esp. not the inside of my MacBookPro.