Battery/Charger Not Reaching Float with Load Attached
It isn't the voltage that triggers the charger to switch to &quot;float&quot; mode — it's the current. The current needs to drop to less than 10% of the CC mode current in order to trigger the mode change. Since your load is drawing 50% all of the time, this can never occur.
Bottom line, this charger is not intended to both charge the battery and drive a significant load at the same time.