First up, for those of you with the Hero 3+, the Brunton All-Day battery pack was a great choice for me. It snaps on to the back of your case and lasts a long time. I don't record constantly, as in I use my GoPro remote and start and stop recording as I see fit during the trip. I maxed out a 32gb card in a few hours and turned the camera off with the wifi still on. The next day, the blue wifi light was still blinking. I heard from a few others who have the Brunton All-Day and some say they wanted more battery life and bought two to switch out on the water. They had much larger memory cards and recorded constantly the entire time on the water. Over all though, I was very happy with it. Keep in mind that it's not meant to be submerged. It has no problem being splashed on so it served as my bow camera where I didn't intend to actually put it in the water. One other thing I would recommend is switching the black O-ring that comes on the Brunton with the white one that is on the back door (that you removed to put the Brunton on). The black one was thinner and let a tiny bit of moisture in as opposed to the original GoPro gasket which was nice and tight.
When I decided to upgrade to a Hero4 Black, the Brunton All-Day was no longer an option since it does not fit. Although, I did hear a rumor that one will be available for the Hero4 in the near future.
My continued quest lead me to what I believe is a game changer. There are multiple pieces and it starts with a 30Pin-to-USB power cable with waterproof backdoor (link).
It's $23.90 + $4.90 for shipping. It fits the Hero 3+ and the Hero 4.
Basically, you just plug it in the back of the camera, snap on the door and shut it like you normally would.
Next you need cable glands (size PG7) and a waterproof container for the battery. For my bow camera I just used a food storage box that I found for a few bucks at Target. I drilled a hole to match the end of the cable gland and screwed it into place I added an o-ring (plumbing section in hardware store) between the outside wall of the box and contact point of the cable gland just for added waterproofing. Then I cut the USB cable about 10-12 inches from the plug and passed it through the gland. Tightened down the gland onto the cable then spliced the cable back together. There are only two wires in the USB cable so it's easy to do. You can look up how-to videos, but I just stripped off about an inch of the outside cable material and half an inch off the wires, slid on heat shrink wrap (or electrical tape works as well at the end), twisted the two wire ends together, and added a little solder (optional) for extra reinforcement. Then you can either wrap it with electrical tape or shrink the heat wrap with a lighter.
I mainly use a YakAttack Panfish Portrait for the bow camera and simply tuck the battery box into the main hatch. The cable is long enough to use extension accessories like the Dog Bone as well and still stow the battery below deck.
I chose two different types of batteries. For the bow camera I got a 10,000 mAh power bank. To give you an idea, the Hero 4 battery is 1160 mAh and the Brunton All-Day is 4000 mAh. The 10,000 mAh battery will last a long time. For the monopod (or YakAttack Boomstick), I opted for a smaller, lighter 5200mAh battery. The keep the weight and bulk down, I used a heavy duty ziplock type bag to keep the battery dry. I added stainless steel washers, neoprene washers and a little contact cement for the cable gland since the plastic bag is flexible.
The E-Case 13 had two slots at the corners so I attached a velcro strap through each one to wrap the battery bag around the pole and keep it in place.
I've taken these set ups on 3 long trips so far and have been very happy with them. I have yet to run out of juice on the bow cam. The one on the monopod runs out after about 6.5 hrs of keeping it on the whole time with the wifi connected to the remote and maxing out a 64gb card (I upgraded the card recently). The new Smart Remote from GoPro lasted about 6 hrs as well without turning it off.
Now if only they made a waterproof microphone for GoPros...