I thought it might be a similar battery to my laptop which has a specific connectot but it's just a slip in cmos battery, probably a CR2032 which I might already have.Maybe you can simply replace it.
And where did you put the rule.
The reason you use /usr/local/etc/devd is so you can easily spot your works. Instead of polluting system rules in /etc/devd.
cat /usr/local/etc/devd/usb_tethering.conf:-attach 100 {
match "device-name" "ue0";
action "/sbin/dhclient ue0";
};
dhclient ue0 after I have attached a USB cable to my phone and enabled USB tether.There is nothing to check on my phone.I'll test this method and I'll let you know.
However have you checked on your phone too?