To increase egglaying make sure they don't run out of food or water. The light needs to be bright enough to read a paper byand for 12-14 hrs/day. You may need to get a lamp timer to make sure they get enough light. Changes in weather and high humidity will decrease egglaying also.
Like Jeepguy, I carry out fresh water twice a day, have two waterers. Water is kept outside of the coop. In the morning, I make sure that the water is warm, to give it a bit longer before freezing. Then, when I get home, I replace the waterer. I don't have any light at all in my coop, so others will have to relate their experience.
A heated water font for chickens draws about 75 watts when on. They have a thermostat in the base with the heat element and are only on when they are cold enough to possibly freeze. They can be purchase in Tractor Supply Company Stores or on line for about $40.00 If you have metal waterers the heated base unit for those is about $45.00, same sources. I know that changing water twice a day is less expensive but doesn't always provide enough water often enough to support good egg laying.
Increase egg laying by adding supplemental light:
Storey's Guide to Raising Chickens says on page 192 (of the new revised edition) that supplemental lighting should be added when natural sun light drops below 15 hours per day.
My input is: Add the light only in the mornings and the chickens will find thier roost normaly as dusk comes on in the evening. A CFL bulb that produces the same light output as a 100 watt incandescent bulb only draws about 23 watts.
So with a good extension cord and about 100 watts of power usage per hour you can keep your girls laying right through the winter. The additional light will slowly increase the laying rate back to pretty much normal, but it may well take 3 weeks to get them there.
The electric cost isn't that great with the light on a timer for 15 hours per day and the water heater running only as needed (depending on how cold it is where you live), if electricty costs 9 cents per kilowatt hour two killowatts comes to 18 cents per day or about $5.50 per month. I think it is worth that to get 24 eggs a day instead of 1 or 2.
The advice about being able to read a newspaper by the light is prety good, if the light is in one end of the coop and you reading the paper in the other end without straining to do so. I would hazzard a guess that your mini-lamp with a battery power source isn't enough light.