Two types tested:

The first meter I tested did not read amps both ways. It would only read when discharging. Volts and Amps were within reason. The shunt gets really hot at 80 amps. See ah-meter1.jpg PIC below.

The second one I tested does not read accurate amps. This is compared to measurements by a very nice and older Empro 100A 100 mV shut I used in series with this. The amps were off by more than 10A and would be worse when in discharge. Volts were within reason. It would show (-) negative amps on the display when charging! (yes, it would say "CHG") They got that totally backwards. The Amp Hours counter would sometimes count up when it should count down. The Watt Hour reading always incremented upwards, don't know how that would be useful. The display is nice but the little battery (battery capacity full/empty bars thing) reading was never right even after a week. The shunt gets really hot at only 80 amps. See ah-meter2.jpg PIC below.

Meter #1 details:
DC 0-120V 0-100A Volt Amp Ah Power Capacity Percent Battery Monitor Watt Meter $25.54
The shunt for this seems to be a 100A 75 mV type
http://www.ebay.com/itm/171806357411 Seller: http://www.ebay.com/usr/elecdesign2015

Meter #2 details:    Model VAC-1200A
DC 120V 200A Wireless Volt Ammeter Power Meter battery Charge discharge capacity $22.88
The shunt for this seems to be a 200A 50 mV type
http://www.ebay.com/itm/232084671168 Seller: http://www.ebay.com/usr/leeshop2016

If the Ebay item number isn't valid here then search for the title.

Other titles: Wireless Digital DC Voltmeter Ammeter Power Meter Capacity Shunt Voltage Current Ah Capacity Meter Charge Discharge AGM LEAD ACID LiFePO4 Li-Ion Watt Meter Monitor Solar Battery Two-Way Multifunction Combo