This is normal behavior.
You may occasionally see your charging indicator lights turn red after they have been green for sometime. This is normal behavior.
Once the battery is fully charged, it will stop charging. However, there will be a trickle of energy leaving the battery (which is good for the battery), which will slowly drain the battery.
Once this reaches a certain level, the charging indicator will turn red and the battery will begin charging again to full charge.
Feel free to contact us if you need any further assistance.