OEM battery life?

[unkl300d]

'95 C280 I'll skip the 'grief with mechanic'
part.... battery pronounced dead.
Original OEM. Five year life span?
Sound O.K.?
I checked the electrolyte level of cells
and two were just below the 'L' shaped
silver metal inside the cell.
The others were just above the
'L' shaped foot. I figured this
thing was the marker for water level.
There was fine halo of brown
dry chemical around the caps.
End of road for battery or end of road for the mechanic?
(the latter is a done deal)
Thanx.

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1979 300D
133K miles
1989 300SE
1995 C280