[Mercedes] Portable battery charger

[dan penoff.com]

I agree with Jim to some extent - I had to “retire” my go-to Sears charger a few years ago when it died. Transformer had an open secondary, otherwise I would have repaired it if it had been a bridge or something easy.

The problem here is that “smart” chargers don’t deal with situations like my W211 “EV” or that Andrew is describing. Reason being is that they’ll typically get the battery charged up along with handling the parasitic draw that you’ve got going, then shut off or go into “maintenance mode“.

Then they don't come out of maintenance mode and the battery dies. I found that with the charger I have now that I listed earlier, if I turn on the charger, select the battery type (standard) and put it in charge mode, it works just fine and will cycle in/out of maintenance mode without shutting off completely. If I just hook it up and let it “decide” what it wants to do it goes into maintenance mode and never comes out of it because the battery is currently chraged from the car having been driven.

-D


> On Dec 14, 2025, at 10:38 AM, Jim Cathey via Mercedes <mercedes at okiebenz.com> wrote:
> 
> For a traditional battery charger I buy: a traditional battery charger.
> Used, at yard sales.  Mostly all you can get new now are 'smart'
> chargers, which will not charge a battery that is too low.  Not useful
> if you left the lights on overnight or something.  (Clue: an LED/LCD
> display is almost 100% a 'smart' charger.  If it has a d'Arsonval meter
> [moving needle] it is almost 100% NOT a 'smart' charger.)
> 
> My favorite is a Schauer.  Has an auto shutoff mode.  Selectable.
> I bought the first one at Sears 45 years ago.  Eventually I found a
> second one at a yard sale so that I now have a backup.  (I'm big on
> backups.)  Both quite old now, both still working just fine.
> 
> My neighbor has a smart charger.  He used to have to come borrow
> mine once in awhile to get the process started.  I eventually found a
> suitable yard-sale charger for cheap and got him his very own.
> 
> For _tending_ a battery, I really like the Battery MINDer.  I now have a
> bunch of them.  At current battery prices, if it extends the service
> life even a year it pays for itself.
> 
> -- Jim
> 
> 
>> On Dec 13, 2025, at 9:37 AM, Andrew Strasfogel via Mercedes <mercedes at okiebenz.com> wrote:
>> 
>> Jump start a dead battery.
>> 
>> On Sat, Dec 13, 2025 at 12:31 PM dan penoff.com via Mercedes <
>> mercedes at okiebenz.com> wrote:
>> 
>>> Depends on what you need - do you just need something to maintain the
>>> battery, or to do that *and* offset a drain/draw on it while sitting idle.
>>> It matters, I know all too well with the W211 “EV” I currently own.
>>> 
>>> -D
>>> 
>>>> On Dec 13, 2025, at 10:19 AM, Andrew Strasfogel via Mercedes <
>>> mercedes at okiebenz.com> wrote:
>>>> 
>>>> My '85 300SD has a battery drain and/or faulty alternator and is
>>> currently
>>>> DOA.  A while back someone posted links to inexpensive home battery
>>>> chargers - would appreciate a repost.
>>>> 
>>>> Andrew
>>>> 300SD Cabernet red
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