Contributed by Scott Monsma (milw)

Have you opened your Dragonfly yet? If so, you will have found a little foil-wrapped rectangular item bearing the mysterious words "FULL RIVER" and a series of code numbers on the other side. Noting that it has a red wire connected to the PCB at B+ and a black wire to B-, you might correctly assume that this is the energy source for the Dragonfly - and one of the major factors affecting the flight duration (aka "fun-time").

I did a bit of Google searching with key words like "full river" +battery, and got a lot of hits for a Chinese company also known as Fullriver, a manufacturer of deep cycle lead acid batteries for golf carts and other mobile equipment. Didn't seem quite the right thing, and in their product list was no mention of tiny batteries. Then I remembered some past mention of LiPO (lithium polymer) batteries as having a very high energy density (power to weight ratio, essentially), so I tried full river lithium battery - and Bingo!

Number one on the list is Guangzhou FULLRIVER Battery New Technology Company Ltd. - "devote to becoming the lithium polymer battery supplier". A-ha! says I, and rapidly jumping to the 'High Multiplerate Discharge Batteries' product page, I see the number two product is the "501417H10C", a 50 mAh, 3.7 V, 1.5 g battery. My Dragonflies battery is marked "501417-HS10C", so it may not be the exact match- but pulling out a ruler showed my battery to be ~13 mm x 16 mm, comparing favorably to the listed dimensions of 14 x 18 mm.

Of interest to us Dragonfly hackers, the next battery in the series is the 452026H10C with more than twice the capacity (130 mAh) and an additional 2.1 g of weight (3.6 g total). Since removing the shell of my Blue Dragonfly saved a tad over 3 g, I think I could reasonably replace the stock battery with one of these babies and be flying for more like 15 to 20 minutes at a time!

I suppose the caveat will be the charging characteristics- the Dragonfly remote is built to charge the 50 mAh battery safely, and the Lithium Polymer batteries do need careful control of the charging current and duration. This will be the subject of future investigations- opening the remote and examining the charging ciruitry- but also could be an opportunity for a home-brew battery charger project. Also coming up- the search for a Full River vendor catering to the hobbyist/home market.

In closing, be sure to scroll to the bottom of the product page at Guangzhou- there is a lot of technical information about these batteries that will definitely be useful in the future!

cheers- Scott

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