Internal batteries

[XKAES]

Undoubtedly, all of the Sony cameras discussed on this board have internal batteries.  Some cameras will function with dead internal batteries, some won't.  And different cameras will use different batteries.  Replacing them when they die may be easy, difficult, cheap, or expensive.  The battery itself is cheap.

On the a900 & a850, the service manual lists the internal battery as a BT901 battery -- and the diagram shows an easily replaced button cell on the AM-015 printed circuit board (underneath the rear cover/panel/screen).

From the Sony diagram, the battery looks like a typical CR2024-type, lithium, button cell, but web searches mainly show the BT901 as a much larger pack of FIVE battery cells. 

Does anyone know anything about BT901 batteries?  Are their different batteries with the same number?

Edited April 24, 2021 by XKAES