Is there any way to get the status of the internal battery this kind of routers have?
maybe some kind of collectd-mod-battery for my TL-MR13U router?
Regards,
If the battery level can be read by the OEM firmware, then there is likely a way that it can be done in OpenWrt, though might require a bit of custom work to read a register that isn't already being read.
You might "poke around" to see if there is already something revealed, such as
find /sys -name 'battery*'
(look under the /sys directory for any file that starts with "battery")