Hi jason910,
I have the same charger you used, but I built it via DIY method (e.g. buy case and battery from Ebay separately).
There are some chargers that provides efficiency of 50% to 60% generally, meaning the advertised rating (e.g. 10,000mah) would only charge up to 50% (or 5000mah for example) compared to your iPhone battery capacity (about 1400mah++), in another word 3.5 times).
Another thing to look into is the use of Li-Ion (18650 sized batteries) or Li-Polymer (can be flat shape) like the batteries used in mobile phones. Generally speaking, Li-polymer has higher capacity and more effective use of space in a charger. Charger can remain flat, which can be a plus factor for smaller capacity chargers (e.g. much more portable).
I have used mainly the 4 Li-ion battery, 2 Li-ion batteries and Li-Polymer battery based chargers. I noticed that the 5200mah Andino I bought has only 45% efficiency (for Apple products it is very low as normally they have 60% from my other chargers). Since I was just back from Hong Kong yesterday, I also saw similar (in fact identical design, same dimension) chargers at the Sim Lim equivalent mall that labeled them as 4000 or 4500mah chargers. 4000mah is more realistic (giving a 58% efficiency). Basically, what I mean is while they may labeled it as 5200mah, the actual performance could be affected by component parts or even unreliable rating.
If you need at least 3 times (assuming 0-100%) of recharge, you would need about 1450mah x 3 or 4350mah of effective charge. If efficiency is 50%, you will need a 8700mah charger. If efficiency is at 60%, you will need a 7250mah charger. But there is a trade off between having a larger charger (higher capacity, heavier) vs smaller charger (smaller capacity, lighter).
In the market, many chargers used a 2200/2400/2600/2800mah capacity Li-Ion batteries or some will use a Li-Polymer batteries. A 4 x Li-ion configuration plus case would weight about 250-280g generally speaking. a 2 x Li-ion configuration would weight about 130-150g. Because of accessibility in Singapore plus being in office, I generally used a smaller pack like the Andino 5200mah (I personally believe only about 4000mah), which is the size of iPhone 4S. Overall gives me more than enough to last for a day of 12 hours of heavy non-gaming, continuous use. For overseas, I would bring along the 4 x Li-Ion configuration pack as colder weather causes the battery to last shorter in the iPhone 5. This is very useful when you have a friend that needs the extra power boast.
