Since buying my Discovery 3 3 years ago if I try to start the engine with the side lights on the vehicle goes into limp mode wont rev the suspension lowers the DSC light shows as does the handbrake fault. Turn the lights off and the vehicle starts normally. Over the past couple of weeks the same problems show up when driving so without warning although generally on an uphill gradient the warning lights come on the suspension lowers if I quickly turn off the ignition then put it back on the engine will bump start and run normally but yesterday whilst driving up the A1 the problem occurred more than 15 times. I thought at first it was a voltage issue but the system appears to run at 13.78 volts according to my code reader. There are no faults showing and nothing appears to come on the display before the Ping. Has anyone had a similar problem?

If thats 13.78 volts with engine running the alternator is shagged, battery could also be on its way to.
On older motors 13.78 is just dandy, but this newer stuff is hyper voltage critical, not just LandRover but many othe rmakes as well, I think 12volt systems are almost at their limit.
Best test is to leave car overnight then measure battery voltage anything under 12.5v dont run engine just unlock and get bonnet up for measuring.

Current advice is any make apart from Denso ( not cheap!) will cause you even more issues