P3D FED Exposure / Battery question

[phil@xxxxxxxxxxxxxxxxxxx (Phil Palmer)]

One of the cameras I am currently running is a FED 'M'.
Although very slightly underexposed the initial films run throught it were
fine.
Prior to going to the Stereoscopic Convention at Llandudno I replaced the
battery. The shots I have had back since the swap have been severely
underexposed - I adjusted the film speed setting to give me another stop and
further films are still severely underexposed !

The initial battery which came with the camera is marked as an 
'AG13 Button Cell' (presumably from the factory) - it was not exhausted when
I swapped it and it registers 1.15v on a multimeter.

The battery I have replaced it with is an SR44 (also known as G13, 10L14 or
EPX76) and is rated at 1.55v.

The question is - Am I using the wrong battery therefore giving incorrect
exposure settings. Anyone know the answer ? - preferably with a UK code number
(and presumably a non-mercury type as I don't think they are easily 
available anymore).

Thanks
-- 
Phil Palmer
Oldham, Lancashire, UK

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The next Third Dimension Soc. (North West) meeting is at Bury, Lancs. on
Tuesday, 16th June 1998.
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