<div class="bbWrapper">How old is the battery? Terminals are usually stamped, week and year - more than 5? Just get a good quality new one, Bosch/Yuasa/ etc.<br />
(I went through all the next bits - with a 9month old battery- which I assumed was ok…<img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f644.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":rolleyes:" title="Roll Eyes :rolleyes:" data-smilie="11"data-shortname=":rolleyes:" />….. many hours later/swear words/ …. Turned out battery had an ‘intermittent’ internal fault.<br />
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Get battery stress/load tested.<br />
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Get alternator checked, if the diode pack fails, the battery can discharge through it.<br />
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if that’s ok, then look at YouTube for parasitic drain tracing/check. For either W215 or W220, basically the same.<br />
It’s a slow and laborious<img src="/styles/mbclub/smilies/wallbash.gif" class="smilie" loading="lazy" alt=":wallbash:" title="Wallbash :wallbash:" data-shortname=":wallbash:" /> job, but satisfying if you track it down.<br />
At each stage, give car 10mins to ‘fully shut down’<br />
IIRC you are looking to have a drain below 60mA, after 10mins, - there is always a tiny drain as it’s active to look for remote key being used.<br />
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best to get a dc mvA clamp meter, and be methodical.<br />
Sometimes it can be the head unit not shutting down correctly.<br />
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check the PSE pump area, and the CD player/amp in boot for dampness.<br />
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Any aftermarket bits? Check and maybe temp detach them.<br />
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Tracker Unit,? Remove fuse.<br />
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It’s infuriating, but wishing you success <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f60e.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":cool:" title="Cool :cool:" data-smilie="6"data-shortname=":cool:" /></div>