What size battery to get? - Benzworld.org - Mercedes-Benz Discussion Forum

ps2cho · 07-29-2010, 11:59 PM

This battery drain issue is just really throwing me completely off. Everything is SO RANDOM it makes absolutely no sense.

So this is what I did...

Car OFF: 12.51v (lost some charge for some odd reason last night. Not normal)

Car OFF Lights ON: 12.51v dropping fast. After 3-4minutes it was at 11.6v (which follows my issues as after a 15-20min drive at night /w lights on the battery will be so low the radio + a/c cut in and out)

That is draining WAY too fast and completely rules out the alternator including the voltage regulator, right? Car barely started. I already load tested the battery and it came up OK..
It makes no 'logical' sense the lights have a problem because then wouldn't the fuse pop? Maybe I just don't understand electronics enough...but that's my thought.
So maybe my battery is failing under heavy load, but is doing ok with my load tester?

So I am going to Costco tomorrow to buy a new battery. If drain still happens, I'll just return it....

...And the reason for the thread....what size should I get?

Thanks guys. Really looking forward to get this damn issue out of my head.

**Jayare** · 07-30-2010, 02:44 AM

Group 49 is the correct size. I doubt it's your battery. If it was, it wouldn't hold during a load test. Aftermarket sound system in the car? Big watt Amp? If so, disconnect the Amp and check for draw on the system. What is the meter reading at the battery with the car running? If it's less than 13.4 volts, your regulator is bad.

Good Luck,

Jayare

ps2cho · 07-30-2010, 05:43 AM

Quote:

Originally Posted by Jayare

Group 49 is the correct size. I doubt it's your battery. If it was, it wouldn't hold during a load test. Aftermarket sound system in the car? Big watt Amp? If so, disconnect the Amp and check for draw on the system. What is the meter reading at the battery with the car running? If it's less than 13.4 volts, your regulator is bad.

Good Luck,

Jayare

Does the regulator....'regulate' when the car is off? If not, then it wouldn't make sense since I didn't have the car on.

I checked my amp and it is definitely off. I only turned on the lights to isolate the problem. Key was not even in the ignition.

A normal system should not go from a 75% charge to a 10% charge within 5minutes.

betapi · 07-30-2010, 06:56 AM

Car OFF Lights ON: 12.51v dropping fast. After 3-4minutes it was at 11.6v....

(which follows my issues as after a 15-20min drive at night /w lights on the battery will be so low the radio + a/c cut in and out)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I'm sorry, but this just screams that for some reason, your alternator isn't putting out, else you wouldn't see this behavior while driving. Battery could be dying from abuse as we speak.

IMHO, YMMV, my opinion is worth every cent you paid for it.

**Jayare** · 07-30-2010, 08:24 AM

Hell man, pull the regulator and take a look at it. It's held in place by two phillips screws and takes about 5 min to pull. Here is what a worn out and new one look like.

Jayare

macdrone · 07-30-2010, 10:32 AM

I would agree with Jayare here ps2cho. The regulator does all the charging to the battery and can inconsistenly charge and ruin it. Thats why you may have boil off and such things like overcharging. Even if the battery is bad the regulator is probably also suspect.

ps2cho · 07-30-2010, 11:22 AM

My regulator is only 3 months old, but i ordered a new one anyway. Should arrive today. Will report back with results.

**Jayare** · 07-30-2010, 12:37 PM

Quote:

Originally Posted by ps2cho

My regulator is only 3 months old, but i ordered a new one anyway. Should arrive today. Will report back with results.

Get a full charge on the battery, start the car and put a meter on the battery terminals. See what the reading is. If it's not 13.4 or better, the regulator is the problem, new or not.

Jayare

ps2cho · 07-30-2010, 03:30 PM

New regulator did not resolve issues...Same issue stands. Old regulator had some slight wear. More than I would have expected from 6 months use. Maybe that points to the alternator?

....but? Why would the battery discharge so fast without the car on?

New update though...It now seems to have jumped from the lights to the A/C. Lights on but everything else off, it maintains 13.8v....
Lights + A/C = 12.4v

At least now I have established it is either A) the battery or B) the alternator.

Its just a damn shame that both have tested OK on load testers.

Why couldn't either one of them just fail the load test so it is easy

Any other ideas on how I can determine which one it is? A new OE battery is $130. Costco does not carry our size unfortunately. Autozone was the only place who carries our size, but it is $100 for 'Durajunk'. For $30 more I could get OE so its a no brainer to me...

ps2cho · 07-30-2010, 06:02 PM

I said screw it and went and got the OE from the stealer. It sure does look pretty

I like how the 'Mercedes Quality' logo is angled on the battery

....

EDIT: Well put it in..No luck. Car starts quicker though. And that's not just because its charged. It definitely started quicker than I have been used to this last year. Gotta be the alternator then I guess

I am now going to replace the alternator. Since I am doing it, I may as well upgrade to the 80A unit (AL66X)

Does the upgrade just require a pulley swap...anything else? Is the connector the same as the 70A?
I want the most painless upgrade possible for both myself and my wallet.