I’ve got a150w inverter , I use a double plug so I can put tv/aerial in, how long do you think I could/should run it with engine off before it starts to effect battery performance ? And will a 300w inverter make any difference getting used for the same thing ? Cheers
What is the capacity of your battery (or batteries) in terms of Amp-Hours?
It will make next to no difference using a 300W inverter as opposed to a 150W job, as the current drawn is pretty much entirely down to whatever you have plugged in.
I don’t have a clue lol how would I find it out? Scania r420 57 reg if that’s any help
Smoggie89:
I don’t have a clue lol how would I find it out? Scania r420 57 reg if that’s any help
Have a nosey at the batteries, they usually say on them the amp/hours capacity.
Don’t confuse the amp/hours with the cranking capacity. The CCA (cranking capacity) is the amps available for 30 seconds at 0 degrees if I recall correctly.
I wouldn’t have thought the power drain of a T.V.would bother the batteries on a truck very much unless you leave it on for hours and hours on end without running the engine. Someone will advise better than I in due course. 
Look at the batteries and read the information on them?
Ill have a look tomorrow now lol cheers, only had it on for the Chelsea match so 2 half hours tops
How long is going to depend on how many amps your tv draws. I run tv and sky box for three or four hours without problem this time of year.
When it is darker and colder and you are using cab light, night heater ect may pay to have some thing to check battery voltage with, think you can get something that plugs into lighter socket, not tried these though.
When it gets to zero degres and below battery performance drops right of, this will be when yo discover your batteries are on the way out.
Thanks for replies people
You only get out what you put in no such thing as a free lunch.
300W is an average current draw of 12 amps but as you are using an inverter you can bang that up to 16/18 amps.Your headlights draw about 7 amps so how long would you leave your headlights on then half it.
Does the inverter have “Low input voltage detection” 
i.e it detects when the input voltage drops below a predefined threshold,
and automatically switches off, in order to prevent it completely flattening the batteries 
If it DOES, then no need to worry 
I’ve got a 300 watt 12 volt inverter have left it on all night before charging my lappy never had a problem, use it most nights with the laptop for up to 3 hrs ish and truck always starts. if you have a weak battery ie dicky cell this can cause problems. just run the truck up for 10 mins before you go to bed just to make sure
wildfire:
I’ve got a 300 watt 12 volt inverter have left it on all night before charging my lappy never had a problem, use it most nights with the laptop for up to 3 hrs ish and truck always starts. if you have a weak battery ie dicky cell this can cause problems. just run the truck up for 10 mins before you go to bed just to make sure
If you are only using it to charge a laptop, it won’t be using anywhere near 300 watts - probably less than half that (reducing to near zero once the laptop is fully charged after a couple of hours).
DoubleQ:
Does the inverter have “Low input voltage detection”i.e it detects when the input voltage drops below a predefined threshold,
and automatically switches off, in order to prevent it completely flattening the batteriesIf it DOES, then no need to worry
all the newer ones have that. a scania will crank with a pretty low voltage left in the battery, but when the inverter stops working in a MAN, then it’s not a warning but it’s acknowledging the fact that now you’re screwed 