Headlight brighter then the Other

My right headlight light is a lot brighter then the left one. What are the most common issues that causes this. I cleaned both lenses. My battery is reading low so I will be replacing that soon. Also both lights just seem to be dim I purchased some silver star ultras and they just dont seem very bright to me. What could be causing my headlight problems.

You have to measure the voltage across the bulb. It should be the same as the voltage out of your alternator. The brighter bulb will have a higher voltage. This means there is a resistance somewhere in the series path from the voltage source to ground in the circuit of the dimmer bulb, and some of the voltage is lost there. A bad ground can cause this, as well as a bad connection to power, or corrosion somewhere in between. Let's say with engine not running, you measure the voltage across the dim bulb and find it to be 10V. Now you can measure from its positive terminal to the battery's positive terminal. This should be zero. If it is not, you have a bad connection to +12. Then measure from the bulb's neg. terminal to the battery neg. terminal. This should also be zero. If it is not, you have a bad connection to ground.

Yeah, are you sure the bulbs are both the same? if one is a 9004 instead of a 9007, the high beam and low beam are switched around.