Pond water oxygenation

Towards the end of last season my little pond was nasty. I bought a solar powered two stone air pump to increase oxygen levels. Being a tight old git I got to thinking how I could use the Solar panel and it,s installed 4xAA chargeable batteries which charge from the sun when theres enough solar energy to run the air pump and charge the batteries. So, during the winter sun days I installed some of my other rechargeables and sat it in the sun. Result...free power to charge batts. I have reinstalled it in the pond a few days back and it's pumping away like a good un. It must be the Yorkshire in me even though I was born in Kent.