Just finished replacing my battery (MacBook Pro 13” early 2015), glad I did, the old ones were noticeably swollen. I was surprised to find the battery at 57% upon completion and charging the new battery. No problems with replacement however, kit arrived without the Pentalobe driver. I got a nice complete kit from Amazon for 20 euro in 2 days. iFixit offered a coupon on any future purchase but right now, I have no plans on needing anything. Nice gesture but would have preferred the driver in the kit in the first place.
Suggest having a small can of compressed air on hand to clean out the interior, after 4 years, mine was quite dirty. Ear buds and alcohol were the best I could do. And a magnetized driver is mandatory I think.