Batt Lo Displayed. I replaced with new batteries. The display still reads Batt Lo and I cannot changed temperature, etc.

Suggest have battery tested.
Most thermostats cost more to repair than to simply replace them.

this is user guide might help you...... http://www.service.braun.com/line/PD/D6005/D6005_2_GB.pdf

Have you tried replacing the disposable-lens filter ?
The manual is available at: http://brauntherms.com/downloads/IRT4020_4520_MNLA_U.0035_OM_25JAN11.pdf

Thank you for your interest with Emerson White Rodgers. My Name is Joselito Laxamana from technical department. After replacing the battery you need to do the reset operation. If you need further assistance please contact us at 1800-284-2925.

Problem:
Temperature taken is not within typical human temperature range (93.2 °F - 108 °F / 34 °C - 42.2 °C).

Solution:
Make sure new, clean lens filter is properly inserted. Then, take a new temperature.

Lo is displayed when the room temperature is below 14F or the heater thinks the room is below 14F, which would be caused by a problem with the room temperature sensor or the sensor is unplugged. 70 is what you have the heater set to maintain. Check the white wire on back of the heater.

Hello my name is Heath it will be my pleasure to assist you. Take the new batteries out and let the display go completely blank then reinstall the new batteries and the lo batt light should go off.

Turn control to off. Remove the batteries for at least one hour. If the display message still reads "bat lo", leave control off, batteries out, and disconnect the red wire on back and wait another hour. Reconnect red wire, put new batteries in and turn system on. It's like a reboot.