BMW E30 3-Series Service Indicator Battery Replacement(1983-1991) | Pelican Parts DIY Maintenance Article
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Sanyo Lithium CR14250 Replacement Battery for E23 E24 E28 E30 E32 E34 Cluster SI-Board - Ivo Christov BMW E28 specialist
My temp gauge and tach were not working so I replaced SI batteries but realised that there is a small repair done on pcb trace and some of the transistors are blown.
SI Board Batteries - Info Please | BimmerFest BMW Forum
BMW E30 - Replacing the SI Board Lithium Batteries - - YouTube