Initially why not run an extension lead to your laptop
? Make up a 12V one if necessary.
A laptop, particularly when charging
a fully discharged battery
will take a fairly large current
draw for quite a few hours. 12V wiring for this would need to be properly sized. If it were me I'd make it quite substantial.
My understanding is that each laptop needs a different voltage so unless you're using a DC-DC converter the 12V system may not suffice.
I've found that most computer use takes place in the marina so marina power is used. Those very few times that I've needed to recharge the batteries
of my laptop I've used a small 300W inverter
and the laptop charger
If flexible use is that important why not use a tablet? Many have excellent battery
life (way past that of a laptop) and if charging
is needed then an inverter
matched to the charging supply would do the job. There are many different types so matching one to your needs may not be that difficult.
I've used cigarette lighter sockets and plugs from a reputable maker for my 12V outlets. Poor quality ones are certainly not up to the task (don't ask...).