Well, as always, first there's a need and then a solution has to be found to fit that need. This time it is about power, power for my photo camera to be precise, a Canon DSLR, model quite irrelevant as what I'm writing here can apply to the whole range and even other manufacturers that use similar systems.
I do a lot of "off grid" traveling into remote locations far from any viable sources of electrical power, power that would allow to recharge the batteries so that can only mean the need to carry lots of batteries. That does add some extra weight, some dead times checking the power level and making sure I'm not going into "action" with an almost dead battery but the worst thing is that it doesn't solve the problem in time lapse photography. You would normally squeeze a few hundred RAW shots out of a battery but that number drops a lot with the outside temperature.
In order to solve all these problems I needed something to boost my power capacity without turning to an expensive and rather useless battery grip. They change for the worse the handling of the camera in wildlife conditions and do do a lot of extra good for time lapse. So the only way out of this is external power. Since cameras don't have plugs for external power (as flashes do for example) it's a little bit trickier to tackle.
I wanted to go cheap, I wanted to go light and I needed something rather simple and reliable. That's why I had to turn my head once more to China and main stream products rather than dedicated solutions. I power it all from a nice LiPo (that stands for Lithium-ion Polymer and it refers to the battery's chemistry), the kind of one used in radio controlled "toys". Since the final rig would use the same battery for other purposes I chose a rather "huge" battery, this one to be precise <link>, a ZIPPY Flightmax 8000mAh 3S1P 30C. To break it down for you outsiders that means of course 8Ah capacity, 3 cells in series and a 30C maximum discharge rate. All that we care about is the 8Ah capacity and the roughly 12V given by the 3 cells specification which sum up to about 96Wh of energy.. compare that to 12.9Wh that a Canon LP-E6 holds. Numbers should be taken with a big grain of salt as they're just good for comparison and don't hold up with real life.
To adapt from 12V to the 8V needed by the camera a DC-DC adapter is needed. To build one is quite a hassle, to buy a dedicated one is quite expensive but in a spark of genius I had it, I could use a simple and cheap car adapter. They are used to plug into your car's cigarette plug and power phones and such from it. I found one easily and after removing it from it's original case and moved it into a much smaller one I was one step from my goal. The only thing that was missing was the link between the source of power and the camera. For that I needed a battery adapter, the kind of adapter used to power your camera from the mains. The genuine one is way more expensive than this project's budget but you can easily find ebay clones for a fraction of the cost.