Westfalia A2S18 Original Instructions Manual page 25

Operation
However, over time the battery's performance can deteriorate. If
necessary you can purchase a 2.0 Ah replacement battery under the
article number 87 84 74, a 4.0 Ah replacement battery under the
article number 87 84 75 and a 5.0 Ah replacement battery under the
article number 94 24 56 from Westfalia.
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