"My recommendation is for everyone to get a cheap plug in the fag lighter voltmeter even if just to get a feel for what normal looks like." Electrical problems are clearly common on Sevens. I agree that it's smart to monitor a few simple things in the same way that we do for tyre pressure and level of coolant and engine oil... and battery acid where appropriate. I suggest that the basic set is the battery voltage at rest, minimum during cranking, and at 3,000 rpm. It's then a lot easier to spot deterioration by comparison with previous values. I'd recommend a multimeter because it will do other things, but you can measure those voltages with a small digital voltmeter as John says, and there are also some units that provide a cigar lighter socket, one or more USB charging sockets, and a similar voltmeter. I was concerned that those little voltmeters might be overdamped and that they couldn't be used to show the transient minimum during cranking, but with a sample of 2 (!) that hasn't been the case. (This is a separate issue from the much shorter transient drop that Andrew Revill identified as the problem with a certain type of starter. That required an oscilloscope.) Jonathan PS: As always I'm happy to supply wiring diagrams for Sevens and to recommend a multimeter.