I have not noticed a slow down on my SE.... I cant keep the battery charged long enough. Phone worked perfectly on 10.3.2 on November 27th, 2019, battery lasting all day and charged by my bed overnight along with my work iPhone (wake up in the middle of night and swap phone charging). On 11/28 I was notified by my bank that as of 12/4, I needed to go to IOS 11.0 or later in order to use the mobile app. Could not select any iOS other than 13.2.3. So I blindly updated to IOS 13.2.3... 1st mistake, did not perform a backup. iPhone bricked - stuck in endless reboot cycle. Only option was to do a forced update via computer. 2nd mistake, last backup was 1/3/2019... lost all messages between then and now. Photo's going to cloud storage - Notes too - they were safe, but all else lost.
Currently, phone was plugged into a computer all night and the battery was about 78 or 79 %. Phone hot (bad for battery). Unplugged phone, drove to work (15 minutes) checked battery after 1/2 hour - 46%...NO apps running in background except mail. it keeps racking up the unread emails that I have ignored and let fall of (after 2 weeks)... was at 0 emails at 8:00am, now at 10:00am 1,530 emails.
this new OS (13.2.3) is prematurely aging my battery - phone is plugged back in to charge and fetching email every 15min (4 accounts).
Apple has blacklisted all other IOS versions except iOS 13.2.3 - so I cant restore back to iOS 10.3.2 (I have the original downloaded from Apple version that I upgraded the iPhone from.
They have effectively killed my phone by having to tether it to a power source. By the way, with the new battery app, the battery is 87% (13% aged).