A good solar charger controller is not expensive in relation to the total cost.

1. http://www.sunergytechnology.com/th/
A solar charger employs solar energy to supply electricity to
devices or charge batteries. They are easily portable. They are
used to mains-supply charges for energy saving during the day
time.
Portable solar chargers are used to charge cell phones and other
electronic devices as well. Solar chargers can be easily
transported from one place to another and be used by a lot of
people. As the need and use of electronic devices has increased,
thus creating demand for portable power devices to recharge
these devices. Portable solar chargers become the preferred
power source.
A solar charger is best used to charge up a storage battery rather
than electronic device directly. A charger controller is basically a
voltage regulator to keep batteries from overcharging. It helps to
regulate the voltage and current from solar panels to the battery.
They are available in all shapes, features and price ranges.
Solar Charger Controller

2. A charger controller is an essential part of nearly all power
systems that charge batteries. The basic functions of a controller
are quite simple. They are as follows:
- They prevent overcharge.
- Overload protection
- Blocking reverse current
A good solar charger controller is not expensive in relation to
the total cost. They may also monitor battery temperature to
prevent overheating. Some charge controller systems also display
data; transmit data to remote displays and data logging to track
electric flow over time.