Every owner of an RV and off-grid power system should have a good AC/DC Digital Multimeter. Professional grade DMMs (digital multimeters) can cost hundreds of dollars, but I finally found a low cost DMM that I am happy with. This DMM has a clamp on ammeter which has the rare ability to actually measure DC current. This is very useful for troubleshooting solar and other power systems.
EZ-DMM
Module Type: EZ-DMM
Specifications.
Display Count: 2000
Auto Range: Yes
Jaw Capacity: 17mm
True RMS: Yes
Diode: Around 3.0V
V.F.C.: Yes
NCV: Yes
Data Hold: Yes
Zero Mode: Yes
LCD Backlight: Yes
Auto Power Of: Around 15 Minutes
Continuity Buzzer: Yes
Low Battery Indication: 2.5V
Input Protection: Yes
Input Impedance for DCV: 10M
AC Current (A) 2A/20A/100A (±2.5%+5)
DC Current (A) 2A/20A/100A (±2%+3)
AC Voltage (V) 2V/20V200V/600V (1.0%+3)
DC Voltage (V) 200mV/2V/20V200V/600V (±0.7%+3)
Resistance (Ω) 200Ω/2KΩ/20KΩ/200KΩ/2MΩ/20MΩ (±1.0%+2)
Capacitance (F) 2nF/20nF/200nF/2μF/20μF/200μF/2mF/20mF(±4%+5)