DIAGNOSIS The solar cell remote uses Bluetooth, not infrared. Lag or short range is almost always due to interference or a weak battery that isn't getting enough light to charge properly.
FIX First, recharge it. Leave it under a bright room light or near a window (indirect sun is fine) for at least 4-6 hours. The red light on the front should come on. Then, re-pair it. On the TV, go to Settings > All Settings > General & Privacy > Power and Energy Saving > Remote Control Battery Saver. Turn it OFF. Then, press and hold the Back and Play/Pause buttons together for about 5 seconds until it re-pairs.
IF THAT DIDN'T WORK Check for interference. Other Bluetooth devices (soundbars, headphones, speakers) nearby can clog the signal. Turn them off one by one to test. Also, make sure the One Connect box isn't buried behind metal, which can block the signal.
HEADS UP If the remote is constantly dying, the solar/battery unit might be defective. You can try a factory reset on the remote (press and hold the power button for 10 seconds while pointing it at the TV). If it's still bad, Samsung will often send a replacement under warranty for this known issue.