Power to a trailer has half power. There is a baterry on the outside when you hook this up you get full power. From the metter we have a blk, red, what wire everything is hooked up but we only get half power without the battery can you help?

You will have to follow it out, Any relays involved having bad contacts can do this.
Can you describe the circuit?

Yes it's a 75amp metterbox that you plug your trailer up too.when you plug up to the box it only gets half power to the trailer, until you hook up to a battery outside then you get full power.

Are all breakers on? Maybe reset any breakers.
Any Model number and Manufacturer?

What happened to ground?