This subject came up a couple of weeks ago, I think on this list.  The new,
very small/compact jump start batteries.
Well, I got a chance yesterday to try on.  On a very dead battery in my '90
T-Bird.  And the darn thing worked!  Actually three times!  And according
to the meter on the thing it was only pulled down about 20%.
One of these:
<
http://www.amazon.com/Spirit-G03-Emergency-14000mAh-Saunsung/dp/B00KCBCXKC/ref=sr_1_1?s=automotive&ie=UTF8&qid=1417808523&sr=1-1&keywords=spirit+battery
>

So, I'm impressed.