Here's an excerpt from an article I wrote for Control Line World a few years back. I am still using the box and I can get an entire season out of four "D" cells.
"Gadgets!!! We all love them and while some are just cool and somewhat useless, there are those that really do work. That glow plug perched on top of the cylinder head is a great little item as long as you have a means to light it off. This brings us to igniters. The two most popular are the rechargeable Ni-Cad drivers that attach directly to the plug and the good old 4-cell hobby battery, the latter employing a plug attachment device connected to the battery with a wire. They both work well until the inevitable happens: You forgot to charge the Ni-Cad or your hobby battery shorted out and it’s completely useless.
Enter the B.L.R.B: Bob’s little red box.
Simply stated, it’s a holder for four “D” size dry cells that are set up in parallel (1.5 VDC total) and very easy to change. Furthermore, it has a simple phone jack that allows use of a number of different glow plug connectors or alligator clips. Check out the photos.
I fabricated the box from some 3/16 plywood, glued and pegged. Note the partition that keeps the cells in place. I then soldered four little compression springs to a brass strip and using a short length of wire, connected the strip to one terminal of the phone jack. The springs bear against the negative ends of the cells. Another strip without springs engages the positive ends of the cells and a short wire connects it to the other terminal of the jack. The two contact strips are attached with small screws or bolts. Now, get yourself a mating 2-pole phone plug, wire up your glow plug connector(s) of choice and you're in business. The piece of string that goes under two cells makes them easier to remove. I picked up some little brass hinges and clasps at the neighborhood hardware store but any means of keeping the lid closed is suitable. A small piece of foam under the lid keeps the cells in place. After you build the box and install four cells (I use ONLY the Eveready Energizers) you’re set for a lot of use before they need replacement. Also, you should pick up a spare pack of four new cells and keep them in your car. When the originals need replacement, it takes about a minute.
A few more things to mention. Note how flat the box is – it just slides comfortably under the wing. Also, you can choose other sizes or numbers of cells. Two would probably go for an entire season or, for that matter, you could use “C” cells instead. Just tailor it to your flying needs."
You get to the field, your battery’s dead – NO PROBLEM. Just go to the local drug store or Walmart and pick up four Energizers (NOT Dura-Cells)