Portable jump starters/power packs, less power than claimed?

[Justin Smith]

I have moved this question from one originally in the Auris forum (here) but which is not really Auris specific any longer.
To summarise, I was advised to buy a power pack rather then mess about trying to get a 12V feed - from the cars "cigarette lighter" 12V outlet - whilst the ignition was off (which I needed to recharge our camping stuff).

I would be grateful if the esteemed members of this forum could check my figures here !

I bought a Gooloo GE2000 with supposedly 10,000mAh capacity, though rather inconsistently it says on the box it has 66.6WH Battery capacity (10,000mAH at 12V would actually be 120Wh, not 66.6 ? ).

I tried it with my NiMh Battery charger linked to the power pack's 12V output but was shocked how quickly it discharged.

So I took it to work and tested it.
I set up a 17 Ohm load from the unit's 12V output and monitored how long it took to discharge the GE2000.
I calculate a 17 Ohm load at 12V should absorb about 8.5 Watts, though in actual fact the average voltage over the test was about 11.2. But even 11.2V into 17 Ohms should be 7.4 watts.

So, if the GE2000 really does have 66.6 Watt hour capacity it should take 9 hours to discharge ?
It didn't, it was flat in about 2.5 hours, by which time its output was down to only 10.4V (would that actually power a Battery charger requiring 12V ? ).
2.5 hours at 7.4 watts is about 19 watt hours, less than a third of its claimed capacity of "66.6 watt hours"...... 

Also, when recharging it with its 15V x 1.0 amp charger (= 15W), it should take about 4.5 hours the charge (66.6 divided by 15).
It didn't, it reported it was 99% full after only 90 minutes. It never moved from 99% for a good hour after that, but switching the unit off and on at that point brought up 100% so I am assuming that was just a software issue (it may not register 100% whilst charging till it's rebooted ?).

Am I right, the unit is way down on power ?