I doubt it's OMWeather or the connection setting (unless you're out of range of wifi and it's searching for a connection). I have OMWeather running and updating every hour. I leave my N800 connected to wifi 24 hours a day. The battery lasts for several days in sleep mode with OMWeather still updating. I don't know how many days because I use it a lot and usually charge it every night, but I've gone 4 days without a charge.

I had a similar battery drain problem, only I was dual booting to a cloned OS on the internal SD card. It worked fine for a few weeks and suddenly started using all the battery in a few hours. I had made some changes and installed a few new programs, but even undoing all that wouldn't fix it. I reflashed the OS several times and restored from an old backup, but the battery still drained. I finally reflashed and didn't restore from a backup and the problem is gone.