I opted not to accept the particular brand that they replaced it with, went with another brand (more expensive than the original) which they were happy to credit back and sell the new one (went from Whistler GT-438 to Uniden LRD950). New one hasn't yet exhibited any adverse symptoms.

I did wonder if it was something to do with the power but I had my satnav loaded into the lighter before the radar and the satnav was fine, so I doubt it was the power.