Our 12 volt TV sets are backed by a full 12 month warranty.
There are certain minor exclusions to this, where the TV set has be subjected to incorrect voltages, or if it or any of the accessories have been modified in any way.
As we sell our sets with a dedicated voltage regulator as long as this is being used in the circuit then all should be well with regards to voltage fluctuations.
The regulators themselves, if sold to you without a TV set, are sold as a spare part and not covered by a warranty. Equally if they have been modified in any way (e.g. changing the plug) they are not covered by a warranty.