# Posted: 20 Aug 2020 12:16
I don't think my brain works in this way so looking for some help! I've been on a steep learning curve...
I am about to buy some land where I want to spend some time, but its off grid.
I want to be able to work and have a cool box so I want to have power. Its a shaded area so I don't think solar is really an option.
What I think I have worked out is:
If I buy a car battery - say its 100amps
Buy an inverter (seems to be lots of them around, not sure what wattage I need - will come back to this).
If a laptop charges at 2.5 amps, and a cool box at 3.5 amps then I would get 16h out of it? (100/6)
(not worried about the exact figure, appreciate there is a drop off and the coolbox only runs when it needs to)
Is that right?
Does the inverter draw power that I need to consider?
Next is charging the battery.
If i get a splitter put in my car off the alternator and its an hour drive there and back (so it would be charging for 2 hours) would the battery fully charge in this time?
Back to the inverters, they seem to have different watts.
If the coolbox is 12w and the laptop is 2.5a x 15v = 37.5w total say c.50w - is this the level of wattage of inverter I need? - they seem start at about 300w so thats throwing me and should be more than enough. Does it matter what inverter you buy - can I get a cheap one?!
Would also use it to charge other electrical devices, maybe power a light / radio, but all low level stuff I think.
If I can understand the maths then I can work it out so am looking for confirmation that I understand it correctly!
Thanks in advance!