Elk Buster
I've gotten so much from this forum, and others, I felt I needed to share back.

This is my 3.7V Li Po (Lithium Polymer) external.  The battery is rated at 4000mah.  That's about 5.4 times the size of the J10's internal battery.  I bought the battery from eBay really cheaply, so we'll see what it really turns out be be capacity wise, but so far I've run the battery in the field for 2 weeks and it's taken about 200 photos and is still going strong, about 130 of those photos have been with the flash.  It's still pretty rainy here in Oregon so it's still pretty dark.  I use this type of batter in my RC planes.



I added a fuse holder with a 3 amp fuse on the positive side just in case any water shorted things out.  The battery will safely discharge at up to 60 amps without hurting the battery.  That's what the 15C means. It means the battery can discharge at 15 times the capacity, 4000ma x 15 = 60,000ma or 60 amps, about a quarter of what a small car battery can do, but in a much smaller and lighter size.  The three amp fuse lets me charge the battery without having to switch the fuse, otherwise I'd go with something less.  (My charger only charges at 2 amps/hr max.)



I used a couple of small tabs of Velcro to secure it to the inside lid.



The connector I"m using is called a Dean's Ultra.  It's rated at some wild amperage, maybe a 100 or so.  Way more than will every flow through it for trailcams.  But I used it because my charger is set up for this connector and it was only about $3.60 for a male/female set.  You put the female plug on the battery so the chances of shorting it are greatly reduced.  I get these from my local hobby shop.  They have many other types of connectors.  I happen to be using these so I stuck with it.

I wanted to go cheap, so I bought a 11.1V 3S battery from eBay for about $14 shipped.  That's three 3.7V cells in series.  I split the pack into one 3.7V battery and one 7.4Vbattery.  I plan on using the 7.4V battery in my next build to power the AIO and the slave.  I'm hoping the extra voltage won't be too much for the V2800 that I plan on using.  From everything I know about auxiliary battery packs for pro photographers, I think 7.4V won't be a problem, but of course I'll let you know one way or another. 

If I was to buy more of these batteries for trailcams, I'd buy from HobbyKing.com.  I've bought batteries from them in the past with great luck.  I'm not sure I trust the eBay batteries.  I'll post here down the road to let you know if I get the full 4000mah or not.  If it works out, I'll be happy, but if not, I'll spend a few extra bucks from a company and manufacturer I can trust.  

Here are some pro's and con's to Li Po batteries:

Cons:
Need a specialized charger that can handle Li Po (max 4.2V and 3V cut off) or you can damage the cells. (About $50 for a good one at HobbyKing.)
They can be physically damaged more easily because there is no hard outer covering (Though you can get them with a hard case.  They are used in RC electric cars. But they cost more. )
Need to be careful charging because damaged cells have been known to explode violently.  (Search YouTube if you're curious.)

Pros:
Good capacity for size.
Cells are flat so they can more easily be put into a smaller, thinner case.
LSD  (Low self-discharge.)
About 700-2000 recharge cycles, depending on brand.
No real memory effect. 
Safe if not damaged.
Operating temps are within most people's ranges, except for maybe you guys up in the Great White North.
They are the correct voltage range for all cameras that use 3.7V lithium ion batteries.
And, for me, I already had the charger. 

I hope this gives you an alternative way to do an external power setup, or at least some food for thought.





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