I am till experimenting with cache batteries. Latest findings ...
I have recently tried two different batteries with some success. Bearing in mind that the Powermonkey Extreme (PME) battery will not charge directly from The Plug II, a cache battery is required. Before buying I searched 'Googleland' with the following criteria:
A: 500mAh input to meet The Plug II output and to begin charging at a lower speed
B: 0.5mA - 1.5mA output from the battery (1 - 1.5mA output is required for the PME and ipad/iphone type devices etc)
C: 5V input and output
D: Integrated solar panel if possible
E: Minimum 2600mAh capacity, more the better
After much searching, I went for the following two units ...
1:
http://www.ebay.co.uk/itm/330545334309?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l26492:
http://www.ebay.co.uk/itm/151129762853?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649The first device is 5V/500mA input and 5.5V/800mA output. Capacity 2600mAh. £10.95
The second device is 5V/500mA input and 5.2V/1500mA output. Capacity 5000mAh. £16.95
Both have a 0.7 Watt inbuilt solar panel and lithium-polymer batteries. They are available worldwide.
I tested both when charging from the mains (120v-240V). Both units can be charged from The Plug II at about 11 km/hr (further testing required). They both allow 5V USB charging while charging an attached device (any 500mA input device such as Steripen Freedom, ipod, Petzl headtorch etc).
The second unit, the 6000T Pocket Power, can also charge iPhones etc due to it's 1500mA output. It seems to be a better choice if you require ipad or iphone charging ability. I like the first device but capacity was lower and output insufficient to charge my iPhone.
Looking more closely at the 6000T Pocket Power, charging from solar takes 8-12 hours and from mains/computer via USB port 6-8 hours. The charging indicators are good and it seems to start trickle charging from the solar panel on very dull overcast days. So far so good! At £16.95 it is good value too.
More info here (manufacturer's wholesale site I think) ...
http://highway-technology.en.alibaba.com/product/737792905-213190392/Highway_Emergency_6000T_pocket_power_supply.htmlAs I mentioned earlier in the post, my PME was nicked from a camp site this summer. I was meaning to replace it immediately but thankfully held off. I have only just discovered that Powertraveller revamped the PME in March 2013. It now comes with a 5V USB output and a 12V output for camera batteries etc. This is good news as it makes the PME compatible with any 12V system.
Original version of the PME on sale at the time of writing ...
https://www.powertraveller.com/en/shop/portable-chargers/outdoor-adventure/powermonkey-extreme-5v-only-version-1:1/New post-March 2013 PME 12V version ...
https://www.powertraveller.com/en/shop/portable-chargers/outdoor-adventure/powermonkey-extreme-12v/Here is my thinking ... the 6000T Pocket Power can be charged from The Plug II during the day when moving, or by solar when stationary. As it can charge another device while being charged itself, the PME could be attached to the 6000T Pocket Power as a suitable en route cache battery. This may solve the problem of how to charge a higher capacity storage battery from The Plug II as the PME will not directly charge from The Plug II.
In summary the PME can be charged from mains/solar/6000T Pocket Power (hence from The Plug II). The 6000T Pocket Power can be charged independently from its integrated solar panel. The main solar panel is a Goal Zero 13.5 watt providing a 12V car adapter output and a 5V USB output. As I have standardised on 5V USB chargeable devices and 12V devices (such as camera battery chargers), this looks like a step forward.
I have yet to test the final set up on long tours but will post results here in future.