Sounds like your charging system may not be working. Put a volt meter on the batt and find out how many volts. You say it's been raining that may be enough to make the fan belt slip causing the no charging. so check that first. Looking is cheep

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1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)