all the 2000s are like that. the center is probably the ground for the meter. they also have 3-4 power leads.
0.3 amp I'd probably just call that an error unless you confirm the draw with another amp meter (inline, not clamp). they are getting old. I have seem them read that even with the shunt wires disconnected and shorted to each other.
unless you confirm there is draw with another meter I would just ignor it. you might have to manualy reset it every so often to not get a low battery alarm
which will happen over time as the start AH drains on meter.