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You make a very good point I hope to illustrate with one scenario. A bit off topic, because our cars are all 2 series Volvos, but the basics of battery charging still apply.
I had a situation for some time (12 years ago) in my 300K+ commuter car where I felt the alternator was not handling the load of driving with wipers, heater, defroster, and headlights along with replenishing the cranking drain at a reasonable rate.
The voltmeters (2) indicated charging rather than discharge, but I could not be sure the battery wasn't sulfated to the point where the charging current never rose to load the alternator. Or were the three-pulley belts glazed and slipping when the load was there? An ammeter will tell you this at a glance (although the picture below wasn't that particular glance).
Of course, the 240 is especially problematic for an ammeter unless the wiring is modified to bypass the starter. A lot of 8-gauge wire later and I had the information I was after (the belt was silently slipping*) but I wished I had a zero center milliammeter to install with a shunt, because running all that stiff wiring into the cabin to a cheap tin ammeter is a prescription for fire unless every detail is anticipated and cared for.
When I took it all out, the firewall grommet did not get plugged, and that 3/4" hole was enough to allow several mice to gain birthright citizenship under the carpet.
I still use voltmeters, one digital, and have learned to follow the temp comp curve of Bosch's EL series regulator with them, but a zero-center remote shunt-sensed ammeter with the decor to match a PV would seem to be the right thing to have in a PV.
* The slipping belt under load without squealing: finally proved this by connecting a speaker to the "W" terminal (used for tachometer output on Diesels) but the ammeter was enough to alert the marginal charging current.
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Art Benstein near Baltimore
Don't let people drive you crazy when it is within walking distance.
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