I've fitted a digital volt meter
Here is the 'how-to'. Open door, sit down, remove cigarette lighter (if still present), insert digital meter, align as required.
It's a key controlled socket so with the ignition on you can read the battery voltage and when running you can see the alternator output. Useful? Certainly more useful to me than the lighter.
I bought this one via Amazon for £2.54 delivered (it does take a few weeks) although there appear to be identical units for even less money.
See: https://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=well-goal+mini+led+volts&rh=i%3Aaps%2Ck%3Awell-goal+mini+led+volts
Richard
1.8i Mk2 Solar Red, 16 inch square spoke wheels, MGFMania hood with zip-in glass rear window, DRLs, Kmaps ECU, Pipercross panel air filter, MGOC Supersports back box & some cockpit bling