couple of minutes

I have a few volkswagen solar panels, those that they use to keep the batteries charged.
I´m planing to use them in combination with a car battery and a small power inverter with a timer to pump water only a couple of minutes a day to water my bonsais,
I have the panels, the battery, the timer, the power inverter and the pump,
What else do I need to make it work?
A friend told me that I have to prevent the energy from going back or something to shut off the timer when the batteries are charging. Thanks!