Watering a greenhouse on allotment site

I have a lifeline on my allotment- my greenhouse. Now whilst watering at this time of year isnt so much a problem, during the summer I had to rely heavily on a fellow attolmenteer, and would like next year to alleviate the many favours I had to ask for, even though he graciously accepted every time.

There is no mains power in the field

Obviously I cannot leave my hose attached to the water constantly.

So I have a tank, with a tap and am looking for a re-chargable battery powered water pump to feed an irriatgion system from my water tank, which I cannot raise high enough to simply use a drip system. 

I go away sometimes for 2 weeks at a time for work, so although I could invest in lots of drip bags and ask the lovely chap to re-fill them I was hoping someone here might have a more elegant solution... and I was hoping to sort it out asap so I have it sorted in advance of another stunning summer!

Many Thanks