I'd say forget the battery powered hose units.
Check eBay, etc., for a used irrigation controller (a four zone programmable one is more than enough, and a lot of people are replacing their old programmable ones with the new ones that are WiFi connected and thus controllable from your phone, etc.). Plug that it into an outlet, run the output wires (low voltage, so they don't have to be conduited or anything special) a Orbit or Rainbird solenoid irrigation valve. Then use some NTP-to-hose end fittings to attach the valve to your hoses. Program the controller with your preferred watering schedule, and Bob's your uncle.
The Orbit / Rainbird solenoid valves are very durable. If the solenoid fails (I've had a couple fail after ten years or so), it's a $9, two-minute replacement of the solenoid. I'd suggest putting the valve in a container of some sort or wrapping it with something sunproof, as UV rays will degrade the plastic of the valve over time (they are meant to be buried, after all).
Of course, the best thing would be to hard plumb live water to near your garden, and have a manifold with multiple valves to allow you to use the controller to set up different zones with different watering schedules, etc. But for your purposes, McGuyvering it in this fashion will do nicely, and you can use the parts if you later decide to upgrade.
