Inefficient Battery Charger

There is a 12-volt nominal battery that is a bit worn down and depleted, so its internal voltage is only 11.5 volts. You want to charge the depleted battery using a fresh 24-volt battery. So you rig up a voltage divider to divide the source battery voltage in half, making it suitable to delicately trickle-charge the 12-volt nominal battery. The resulting circuit is shown in the diagram.

Each battery has an internal resistance, as shown, and the colored bubbles represent the terminals (external connection points) of the 24-volt source battery, the voltage divider circuit, and the 12-volt nominal load battery.

As it turns out, this circuit doesn't do a very good job of getting the power from the source battery terminals into the load battery terminals. Define the "efficiency" of the circuit as follows: $\text{Efficiency} = \frac{\text{Power into load battery terminals}}{\text{Power out of source battery terminals}}.$ What is the circuit efficiency, given as a percentage?