Everyone has their preferences. A shunt is the easiest way and Tom's foot of #10 wire is good enough for this degree of accuracy. It is fine for digital voltmeters but I like analogue displays for wind ( digital is ok for battery volts). It is possible to use the simple wire shunt with analogue movements but it requires extra knowledge unless you know your meter reads millivolts. You also need to understand lead length.
There are moving coil meters about with internal shunts up to about 30A sometimes larger. More expensive are industrial shunts, usually 75mV and associated ammeters.
Automotive ammeters are good enough, even the moving magnet things where you thread the cable through a loop at the back are good enough.
A scope has its uses in research but I don't consider it a good choice here, neither do I consider an ac clip on ammeter to be a good choice, maybe that having spent too long in a measurements laboratory has made me realise many traps and pitfalls that others have fallen for.
If you want to measure power into batteries you need dc mean and the best place is to measure that on the dc side. AC measurements will show if you are charging or not but that is about as far as it goes.
Flux