APC battery backup conflict with tplink adsl modem

[vite]

I plugged everything to have everything backed with battery.
I also plugged the phone cord into the apc and then from the apc to the modem.
It makes the signal extremely unstable.
I plugged the cord directly to the modem and it works fine.

Any suggestion on how to surge protect the land line?

[Revalin]

You can get DSL compatible surge suppressors, but DSL modems are almost as cheap.  Let it be your surge suppressor unless this is a frequent problem in your area.