erratic temp in instrument cluster

[Louie777]

Hello all, I drive a 2003 CLK 240 (209) and I was wondering if anyone has encountered this problem and have applied fixes. I recently changed my 3 1/2 year old battery because it ceased to hold the proper charge. After installation, fired up the car and noticed that after 10 min or so, my cluster temp reading had gone up to 120 (normal is 80c or so) . Attached an OBD II scan tool and the reading was 85c ( same reading with CC diagnostic #6 ) while the cluster temp still read 120. Noticed that the cluster temp reading would at times fluctuate fast from 80 to 120 even when the OBD still read my ECT at 80-85c. Fan kicks in normally at 95c without aircon and instantly with. I've replaced the Engine coolant temp sensor but still the problem persists. Engine operates normally and no check engine, temp alert or any other warning in the cluster. I'd appreciate the help thanks ?