I loved my Kyocera Brigadier. The battery would last me a week easily. I am a support person, I rarely talk on the phone, rarely use the internet I use it for messaging and pictures 99 % of usage. I downloaded the software update (firmware thing) and now it will drain a full battery in a matter of a few hours. I can not find anything running that could be the problem. I also noticed that when I plug in the charger the red charging light will come on but after only about 4 to 6 percent charge it will stop charging. So frustrating when you have your phone set the way you want, and it fits the purpose you have it ONLY to have the updates change your phone and you find yourself resetting the phone to default just to get back to square one. I am ALWAYS having to remove the latest keyboard and go back to default because I am no good at typing with the new keyboard. It would be one thing if I was the one installing these issues. Just my two cents worth.
I have same problem with my brigadier. After software upgrade on 11/3 battery drains like crazy. I suspect the Email application. It keeps synchronizing all the time even when synchronizing option is set to Never. I reset software on my phone but it did nothing. I am going to dealership today. Check battery usage and see how many % your email uses.
That might of been my issue because I don't use email so I remove it all together. Mine seems to have cleared up. Not so bad now that I removed or ended the processes I don't use. Hope your issue resolved.