There has been several people looking for a good rechargeable battery to use for a portable fish detector. There has been a technology around for several years but it was not easy to use them safely without a lot of expense. Lately I have been seeing protected cells at better prices. I have purchased a couple of sets of cells and done some testing and I believe they will work well. I have made a couple of battery holders along the lines of the IKEA holder. The batteries are “Panasonic Protected NCR18650B 3400mAh Li-Ion 18650 Button Top” batteries. I found LIionWholesale has a good price for them. The battery holder pictures weighs 2.6Oz. and a set of 4 batteries weigh 6.27 Oz. Should you use 3 batteries or 4 in series?? All of the detectors will work well with 4 batteries in series. Some low power non color detectors will run almost as long on 3 in series. They will run just a little longer on 4 in series but not 30% longer. The newer color detectors that I tested will run much longer on 4 batteries in series than with 3 in series. 

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The mounting clips are from McMASTER-CARR part number 1171A72. Beckson also sells a similar clips in 8 different sizes. I believe the 1 inch size would work best. 
The end caps are one inch “Leg Tips” from Menards. They are displayed in the same area as cane tips. To put the hole in the end use a ALL or ICE PICK to punch a hole and put a washer on both sides of the LEG TIP on a 5/8 6-32 screw. The pipe is a ¾ inch plastic pipe from the electrical department at Menards and it comes in 5 foot lengths. 
protected 3400mAh Battery 

I also purchased one of these CHARGER.

Below is my attempt using 800 mAh AAAs for my Striker 4. I had some schedule-40 PVC laying around the basement and a bunch of appropriately sized hose washers and fender washers rattling around in the toolbox. The wingnuts secure the lugs and compress the hose washers inside the pipe to make a tight seal. Eleven AAAs seemed to be the right number for a day of fishing -- charge the USB brick on the solar panel all day and use it to charge the batteries overnight. Without protection I wonder about the long-term health of my batteries, but I didn't notice any degradation as the week went by and I don't intend to use this more than once a year going forward.