Since the battery in the tablet is not really insanely large, it seems like a good idea to make some tablet cover to compensate for this.

Ingredients:
- full size solar panel (425ma)
- 20.000mah battery
- full size & micro usb out
- V5 step-up
- solar energy harvesting circuit
- switch
- casing

Hope I can get proto/mockup/3Dcadfiles of tablet to jumpstart this project and be ready when the tablet comes out.

some initial experiments


ps. Batteries are expensive.

Since I do not have a tablet yet, I will now do the following assumption: the battery in the tablet is about twice the one in the phone. So, for testing with the phone, I need to take half of everything.

First test setup:

How many times (total%) can you charge a Jolla with a 10.000mah battery over usb?

1 x Jolla, starting at 10%
1 x 10Ah battery
1 x Adafruit Solar Lipoly charger
1 x el cheapo 5V stepup

1. charge battery pack till 'done' light comes on
2. discharge phone
3. plug in until phone is charged or batterypack is empty (then goto step 5)
4. go to step 2
5. end experiment, add up %, post results



EDIT: do calculations first... 10.000 mah charging over 500ma takes 20 hours...

That would be assuming 100% efficiency which I'm sure isn't likely.

yes. as a matter of fact it is still charging

but it is hooked up to 1500ma charger and chip limits the flow in the batteries to 500ma, so should charge at that level, but that is obviously not the case.

Battery pack is fully charged.

Connected phone, charged for 10 to 97%.

Now discharging phone phone for second charge cycle. (BT on, wifi on, gps on, installing apps, streaming youtube and recording video, screen on highest brightness)

Charges from 1 battery-pack:
10-97%
5-99%
4-99%
10-99%
10-20%
low voltage light goes on, charging is terminated.

So, 10Ah battery can charge the phones 2.1Ah battery with 375%, making this whole conversion cycle rated at ~80%, which is not bad.

If the assumption is correct that doubling the battery to tablet size and doubling the battery pack to 20Ah gives the same results, you could easily use it for a week with normal use.