I just spent the weekend trying to fix my Android (HTC Sensation). It was running so slow that I got to a point that I could phone out, pick up my phone or write text messages. My battery life was under 2 hours. How bad is that? Actually, I then found that I had a similar problem on my mac when using Thunderbird. The solution was simple enough.
I had 20,000 contacts between my various accounts. There is then a practical limit of contacts on my Android – even when I got it down to 5,000 I was still finding problems.
Symptoms: Low battery life, high CPU usage, unresponsive Messages and Phone app.
# Open task manager. You should see User Dictionary using a high level of CPU %.
# Open People application. Select View. You should see a high level of contacts.
Simple solution: have less contacts.
Actual problem: I have multiple google accounts (personal and couple of work accounts). Somehow two accounts had replicated some users 5,000 times! That is, I have 19,500 too many contacts. It appears to be the joy of Google+ (which I have never wanted in the first place).
Solution: Remove all duplicate users (in this case my contacts were perhaps corrupted because google couldn’t detect any duplicates). That’s right, I had to delete/merge 19,500 contacts 250 contacts a time. Then I had to make sure that I didn’t resync either my Thunderbird or Android.
End result. A working Android, a working Thunderbird and a day of my life lost.
Note: I actually did a factory reset which I didn’t need to do. What I also now have is a very nicely ordered contact list and I know that my backup is working.