Adding an ammeter to my TV

One thing I remember from growing up with a father who towed a camper and was an electrical designer is the ammeter he had in the car to monitor trailer battery charging. I'd like to add one to my TV.

What is the maximum charging rate in amps of two 6V golf cart batteries in series? I found some ammeters with internal shunts that will handle 10A but I'd have to add an external shunt if the charging rate approaches or exceeds 10A.

If I didn't boondock so much, I wouldn't worry about it. However, an ammeter combined with a voltmeter would give me a good indication of the charge state of the batteries and their overall health.

Unfortunately most are 12 gauge.  If they were 10 gauge they would almost be ok.

The Powerwerx wire is "GPT" PVC insulation, bare copper stranding -40°C to +80°C (-40°F to +176°F) low voltage DC power cable.

I would recommend using UL 1015, Tinned Copper stranding, -40°C to +105°C (-40°F to +221°F)   Voltage Rating: 600 Volts. It is sometimes listed as boat cable BC-5W2 (105°C dry 75°C wet) per UL 1426 and meet SAE J378b, USCG, ABYC and NMMA requirements. This is what I use on the trailer for DC and AC. It has the same stranding as the Powerwerx but it does not come as a bonded zip cord. You can get it as a Duplex Marine Cable with a white jacket.

GXL-GENERAL PURPOSE CROSSLINKED POLYETHYLENE, bare copper stranding, -40°C to 125°C (-40°F to +257°F) 60 V DC or less. This is what the vehicle manufactures are using for engine compartment. I will use GXL wire on my truck as soon as the warranty runs out. My Honda only comes with a 12 gauge wire. I will just run a 10 gauge in parallel with the 12 gauge and so the 2 wires will equal close to an 8 gauge.