I have just bought a 1991 300CE and it looks and runs like a dream. It was owned from new by one Swiss gentleman in Zurich and has a full service history, car serviced at the agents and book stamped every 10000 kms ! I think I got a steal. It has now 180,000 kms on the clock and has the feel of a 2 year old ! My question is, the battery tag says it was installed in January 1997 so I guess it must be on it's last legs by now. It is rated at 62 amp/hours and I was sort of thinking the car will run with a bigger battery as I will use the air con most of the time so how big do you think I can go with this. Your advice, as always, gratefully accepted.

BTW, I think I shall hold on to my 500SEL too, do you think I am mad ?

Andy, if you aren't sure about the battery, get a load test done. If that shows that the battery is OK, I would keep it until you develop starting problems. I would choose a battery for its cold cranking capacity, not it's summer reserve capacity. (That of course depends on where you live). In cold months batteries are their weakest. Regarding air conditioning, if your alternator is working properly, a larger battery in the summer months wouldn't really be necessary, IMHO. I find that most batteries are junked because of winter starting problems.

Gary

Andy, I'll second the vote for testing the battery if you want to be sure. Don't replace it based on age. Unless you also notice slow starting, chances are it's OK.

At normal driving speeds your alternator puts out enough current to re-charge the battery and run all of the usual accessories, including A/C. If it doesn't, the alternator and/or voltage regulator need to be checked.

You can monitor charging system performance if you have a volt display in the dash. If there is more current draw at idle than the alternator can provide, the battery makes up the difference by discharging. The voltage may drop a bit. When you accelerate to and drive at moderate RPM, and your charging system is up to the task, the alternator takes over the load and recharges the battery. The voltage goes back up.

Now, if you had an in-dash ammeter, you'd see it move over to indicate Discharge at idle. On acceleration it would swing to Charge, the slowly drop to "neutral" when the battery was recharged. I guess all of this gauge movement was way too complicated for most driver/operators to understand. Some even thought the system wasn't working unless the needle was 'way over in Charge!

So auto manufacturers dropped ammeters some years back.
Oh for the good old days! The last in-dash ammeter I had was in my '72 Duster 340...

By the way, running the A/C puts more mechanical load on the engine (driving the compressor via the belt) than operating the blower motor puts on the electrical system, so don't turn off the A/C just to save the battery. The headlights draw a lot more, and you don't want to turn them off when they're needed!

BCingU, Jim

As with most Benzes the 100AH battery should fit. That size was a option for most MB's. The larger battery will allow the alternator to work less & last longer. At dealer we always ordered 100AH HD battery on roadside cars when they were avail. Now that is a std. size in almost all US benzes.

Agree with MB Doc; been there with my '88 300TE. When my battery went south, I was in the process of replacing it when I found the battery tray to be corroding. I ordered a new OE tray from the dealer, and the only one available would fit either size battery. So, after a little homework and the recognition that there's no downside to a bigger battery other than weight and a marginally heftier price tag, I popped for a humongo battery. I simply don't do battery-related breakdowns, and I live in the frozen Northeast.

Buy the best battery that you can, and forget about it for about 6-7 years.

Best of luck.

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"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo

You can get a cigarette lighter adapted volt meter that tells if your system is charging. I have used one on an old boat I had, which had some charging problems due to the batteries being fairly old.

Then again those batteries are like 3-4 feet long by probably 16 inches wide.

Now thats a big battery.

If you need to replace the battery, you might want to look into one of those new spiral cell batteries, like Optima. I havent used one in my car as it had a new battery in it when I bought it, but if I need to replace the battery, I'll probably go with one of those. I think you can get ones with well over 1000 CCA. In fact they have one thats 1050 CCA.


Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon

thanks everyone,

We have year round mild weather here so the cold cranking issue is not really a worry. I was just sort of thinking of the electrical loading on fans, blowers and the like with the air con running full in mainly town driving. What also bought it to my attention is that my 500SEL has a whacking big 100 amp/hr battery that looks non standard and certainly fills every last inch of the battery tray and then when I look at the 300 I see I could easily squeeze a bigger one in that too. My new car and I are still going through that wonderful, honeymoon type " getting to know you " phase and everything works just fine. I don't want to start worrying about a problem that does not exist, as I see everything is working good so I don't see the need. I have always favored paying over the top a bit for my batteries, a good one last for years and to me is a wise choice..

.....The only job I have to do today I think is change the oil and a filter

again, thanks to all for your ideas