Be warned on those Ring 12v inflators. I had the RAC 635 - and returned it after a couple of uses. Here's the amazon review I left for it, 1/5 stars:
I am in the process of returning this item. It has 3 problems, one of them quite major. In order:
1. I have found that the pressure misreads by about 10PSI. That's a massive amount, and is somewhat concerning as a safety issue. I checked versus 2 other pressure sensors (one digital and the other a traditional gauge on a footpump) which were very close to each other. They measured my tyre at 28psi, whilst this unit told me it was 18PSI. I tried turning the unit off and back on, and unscrewing the connector and putting it back on again as tight as I could. Still said 18PSI. Nonsense.
2. As other reviewers have mentioned, the screw on fixing allows a lot of air to escape before you can unscrew. Not sure why they went for this design.
3. It's a lot noisier than I thought it would be!
So, mainly because of point 1 above, i have contacted amazon and will be sending this back.