Tyre Pump

We keep our van at home and I did have the same problem many years ago but I obtain a small mains/12 volt dc (13.8 volts to be accurate ) power supply so a couple of days prior to going away the van it is plugged into the mains to charge the battery and run the fridge and this of course allows us to plug the power supply into the external mains socket on the van and thus the lead is then long enough to allow us to blow up both tyres also great for when we blow up our air awnings on site when using a hook up of course 

Bit like hard work for us coffin dodgers mm. There are cordless ones out there. I purchased one from Aldi a few months ago excellent piece of kit set the required pressure leave it and it stops when pressure reached. 

Extenders do work after a fashion, but 20AWG wire over 5 metres in total will only have about 10 volts at the end due to a 2v volt drop. So the compressor will struggle in performance unless the car engine is running, even then not totally efficient.

I got one of those, as well and I'm pleased with it.  Bit slow, but that's not a major problem.

I solved this problem years ago,in my grey socket there is a permanent 12v supply,make up an adaptor with a grey plug one end, a 12v cigarette socket, Bobs your uncle,

For those not familiar with them, these are an excellent alternative solution to the OPs request, even for a 78 year old whose caravan tyres require 65 psi.

https://www.halfords.com/cycling/bike-maintenance/bike-pumps/topeak-joe-blow-sport-iii-545399.html

here's the link.

https://www.halfords.com/cycling/bike-maintenance/bike-pumps/topeak-joe-blow-sport-iii-545399.html

My Motorhome tyres need 55psi, I have burnt out 'normal' electric pumps when trying to obtain this pressure so I went to a foot pump.

Trying to pump from 35psi up to 55 psi is like running a marathon, I did get fed up so looked for a better electric pump.

I bought one of these

https://www.halfords.com/tools/garage-equipment/tyre-inflators-and-pressure-gauges/michelin-programmable-superfast-4x4%2Fsuv-digital-tyre-inflator-847159.html

a bit on the large side but very quick and efficient the 12v cable is long enough to reach all 5 tyres (spare on the rear bulkhead) on my 5.3m Motorhome. There is a 240v version if you have that facility.

 if my tyres were going down to 35 from 55. I would be taking to a tyre fitters and getting them checked out. 

One reviewer reported that it destroyed his lighter socket (10amp) because it drew 15 amp and cost more than the pump to replace. I use a mains 230 volt pump for the caravan tyres 60psi