Battery/Charging solutions for sealed devices?

Other Hardware Motors, Mechanics, Power and CNC
1

I'm building an arduino mega2560 based device for long term use underwater, and I'd like to just have a USB port for occasional downloading data and charging the batteries.
This is a low load, but long term device, so it needs a big battery. Very long charge times are acceptable.

I thought a 2s LiPO 7.4V battery with be just the thing, but there are two issues: boosting voltage and balance charging.

There are plenty of 1S LiPo chargers available, but the only devices I've seen for multi-cell LiPos are like my Turnigy Acucell-6. Big and usually plug in to a wall socket. Does anyone know of a 2S LiPo charger I can build in to my device?

Here are some other ideas I had:

Has anyone been down this road before?

2

you can add a coil in the sealed box and place it above another coil on the outside.
Put an alternating current on the external coil and the internal will resonate, resulting in a alternating current.
add some diodes and a capacitor and off you go.

In an extended version you could add a iron core that goes through the centre of the coils.
The iron core preferably outside the sealed box (weight)
This means the sealed box has some hole (seen from outside) for the iron

google: wireless energy transfer system with multiple coils via coupled magnetic resonances
e.g. - http://www.jpier.org/PIERL/pierl40/14.13020509.pdf -

3

You can get sealed, circular power connectors that would work. Really, any power connector could be made to work if you just take the time to seal it (pot it with epoxy, etc.).

Mouser/Digikey/Newark also have plenty of properly-spec'd options as well.

With respect to Rob's suggestion:

http://www.seeedstudio.com/depot/QI-Wireless-Charging-Module-Kit-5V1A-p-1721.html?cPath=1_119