The best batteries are the scud blue dream. Best value for money for me are the japods from dealextreme. Buy an external charger, and try to reduce the usage of the usb to a minimum, it has the bad habit of falling off.

I'd still reflash though, I don't trust ovi suite's update firmware function, and all the problems you describe seem software related. Make sure you flash both rootfs and emmc. You can use backupmenu for backups, it saves the device state completely.

It could also be a corrupted fat partition, it gets easily corrupted and might slow things down. Plug your phone to your pc in mass storage mode and do a disk error checking on it.

And welcome to maemo.org