500 . . . per their website:
D1.Which shunt should I use in my system ?
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The two choices are the 500 Amp/50mV shunt or 100 Amp/100mV shunt. The most common choice is the 500A/50mV shunt. The deciding factors are the MAXIMUM amps that you will either charge or discharge with your system, and the highest "amps" resolution that you want to see on your meter. Usually this is determined by your maximum loads on the battery.
The 100A/100mV shunt will likely overheat if your system if charging or discharging your batteries over 70 amps, so in that case you should use the 500A shunt. Going over this value will not harm the meter--however the shunt can overheat with too many amps. If you have an inverter, converter, or loads with a 12 volts system that exceed 800 watts (or with 24 system 1600 watts) then that will likely put you over the 70 amp limit. For example, using a microwave would usually exceed 70 amps in a 12V
system. With the 500A/50mV shunt you will be able to read "amps" values down to 0.1 amp. A 0.1 amp draw in a 12V
system would be represented by a 1.2 watt load. With a 24V system it would be 2.4 watts.
If you have a smaller system there is an advantage of the 100A/100mV shunt, in that you will be able to read amps values on the meter as low as 0.01 amp instead of 0.1 amp. This would hardly matter in a large system, but in a smaller system you may want to able to see really small loads. 0.01 amp would allow you to see loads down to 0.12 watt loads.