Canon Digital Rebel EoS - Have to take out and re-insert battery every time

I used to get ERR 99 after I switched my lens to 35-80. Called Canon and they told me to take out the lens, and battery, rub the contacts with eraser, switch ON and OFF 12 times, re-insert the battery and lens. Which I duly did.

The camera now forces me to re-insert the battery every time I need to use. Once I switch off, it dies. I have to remove the battery and put it back in to re-start the camera. The Service Center Tech says it is going to cost me $200 just for them to take a look and opine!

Is there any other solution - other than either getting this repaired at the Service Center/buying a new one as Canon wants me to?

Any help is appreciated!

Do you have access to another battery? My initial thought is an old weak battery might be causing the issue.

thanks, will try that!

Have you checked the auxiliary button cell, which is used to retain settings while the main battery is removed?