Volt /Ammeter at odds ??
Some people think all the power runs through the ammeter - its not true.
On a car with no modifications, the normal load on the ammeter is zero or close to zero.
The exceptions are when the alternator dies, when starting, and when recharging.
Problems happen when there are non-stock loads, such as EFI, electric fans, etc wired to the battery.
Another common situation was with trucks equiped with winches and plows running off a connection to the battery.
Less common, but good to be aware of is using the alternator to charge a completely dead battery.
Charging Battery with Alternator - Warning