Safety of Using Portable Power Unit for 18V Power Input Device

[Cavum]

Background
I am experimenting with music mixing. I want to be able to record my music while "on the move", that is, not in the house, but in my car, so I can drive somewhere quiet and enjoy my recordings. The kit is pretty simple:

• One Alesis Mixer, whose power input is 18V 500mA
• One Laptop
• One microphone
• One Roland Edirol R-09 Media recorder

The last three would be simply connected to the mixer, but I know nothing about electrical engineering. I would like to connect my mixer to a portable power source, that must have a British Type G power socket.

Query
I found a power station on Ebay which has the Type G outlet:

Would someone be kind enough to confirm to me whether it would be safe for me to connect the three devices to my mixer, and the mixer onto this power outlet for a couple of hours uninterruptedly?

 

[Harald Kapp]

Basically this should work as long as the total load is less than 400W.

The ad fails to mention the capacity of the built-in battery. You need to know hat in order to calculate the time this unit can be used to power your loads.
What is also not completely clear is how the inverter powering the mains outlet is powered. Does it use the internal battery or an external power supply (from a car's 12V power outlet)?

 

[Cavum]

That is very kind of you. I guess this is almost all information I needed and you covered. You seemed to have made three main points:

1. The total load (less than 400W)
2. The amount of time it will last
3. How the inverter powers the mains

On item 1 above, for me to calculate the total load (in order to be keep it below the 400W threshold), is it just a matter of calculating all individual items and make sure they stay below the 400W, or are there other variables that could add up to the total load?

Thank you so much for your time: much appreciated indeed.

 

[Harald Kapp]

On item 1 above, for me to calculate the total load (in order to be keep it below the 400W threshold), is it just a matter of calculating all individual items and make sure they stay below the 400W?

Yes, easy as this: add the power consumption of all loads, ensure the total is less than 400W.

 

[Cavum]

Thank you. "Safety first": I am more confident on how to ensure I do not fry my kit, and my car <^_^>.