A lead acid battery can deliver massive amounts of current and therefore doesn't need stabilising. The only time the voltage will drop is if the battery is flat... Or if there is a short circuit (fire extinguisher on standby hopefully)
A stabilised or regulated power supply supplies continuous 12v dc to the appliance. A battery voltage will start at 12.6v fully charged & go down from there as battery runs down.
The expensive TV presumably can supply stable 12v via a regulator from a non regulated 12v source, ie a battery whereas cheap TV for its 12v operation bypasses mains to 12v dc regulated power supply & supplies unregulated supply direct from battery hence the problem?
Discounted Insurance Quotes for UKCampsite.co.uk visitors! Up to 12.5% off!
The tv's circuits would have to be regulated at a lower voltage then if that were the case... but the point I have been trying to make is that 0.6v difference in the supply voltage is absolutely negligible to the tv's operation. It is more likely in my opinion that other equipment in the caravan is causing 'noise' on the 12v supply (or even through the receiver) which is interfering with the tv's sound circuits.
anything designed to run off 12 volts if its any good will have fairly wide voltage tolerance maybe 9 volts to 15 volts.. a lead acid battery assuming its not under a very heavy load dosnt really go from a max of 12.6 and then down.. it should maintain 12 volts or close for most of its charge..
under no load a lead acid battery after its lost it surface charge will read around 12.6 volts.. if it reads 12 volts (no load) its near to flat and ready for charging..
if the battery or wiring isnt much good there will be a voltage drop but this shouldn't really happen if the wiring is good and the battery has plenty of charge in it.. some things will just run slower (or dimmer) with less volts but other things may not work properly..
but there are two answer to voltage.. build a power supply that never varies or build something that is able to tolerate voltage variations..
water pumps do draw a fair bit of current.. with less than a good battery or wiring other things will see a voltage drop when a tap a is turned on..
Andysueandsidthedog - trust me if it uses a transformer to step down to 12v there is a good chance of frying the circuits. It is not suitable for use with a 12v battery.
------------- A barman is just a pharmacist
with a limited inventory