HeissRod

For the past 6 months or so, my car has occasionally been sluggish to start and would display the "Convenience features unavailable" message. Within the past two weeks, it's been getting more frequent, so I started measuring voltage this morning.

Main battery -
- 11.8 after sitting for a few days
- 14.0 while car is idling

AUX battery -
- 13.2 at rest (after moving car to be able to get to the AUX battery)
- 14.1 while car is idling
- 12.7 at rest after 45 minutes of being parked

If the main battery is going bad, wouldn't it have gone out over the past few months? Is this a sign of something else causing the main battery to trickle drain?

kponti

Yes main battery is going bad, may be good to replace both batteries and the voltage regulator if you haven't done so. They all seem to go right after each other

Also the drastic change in temp tend to make things worse for an aging battery. If stock, replace soon before it places excessive demands on your alternator. The newest stock battery in these cars are no less than 8 years old to put it in perspective.

HeissRod

Are aftermarket alternatives fine, as long as they are AGM type?

It is an MB battery. The only thing that looked like date code I could find was a Q09 sticker on the top. If the 09 signifies 2009, that was a year before I got it.

kponti

So 5 years old, not completely dead but dying, makes sense

G_Money

Any recommendations on batteries? Mine is on the way out as well, dealer quoted me $350, but there has to be a less expensive, premium option out there.

HeissRod

Autozone has an Duralast Platinum AGM battery for our cars for $179.99, just not sure about the opinions of aftermarket here.

vietjdmboi

I just replaced mine with a bosch from pepboys for $150 with the coupon.

G_Money

Do you remember what it was without the coupon? Or do you have a coupon to give

Also, I saw a Duralast 900 CCA battery at Autozone for $170 iirc, is that fine to use even though the OEM product is 850? the 900 was the closest i saw to 850 that they had.

HeissRod

Make sure it's an AGM type

cetialpha5

Just go to pepboy's webpage. It's fall25. Advance auto also sells it for $189, it's also a 900 CCA battery. A higher number is better than a lower number so it's better than OEM. There's a few codes out there, WD47 or MISSUM42 both take $50 off orders over $125 so it makes it $139. Most stores also install the battery for free. Also the best deal is on an agm ACdelco 49 battery at Amazon, although right now it says out of stock. It's $145.79 but there's a 25% off coupon on the web page which brings it down to $109.35 and it's free shipping. That one is only 850 CCA though.

mrweelr

+1. Just replaced my main with the Bosch 49 AGM from Pep Boys for $150 or thereabouts with my core trade. I also ordered a new genuine MB sealed accessory batter off of eBay with a 2014 date stamp and the car is running smoother with the new batteries. I just replaced them as preventative maintenance, these cars need good strong batteries.

SPatykAMG

I have the regular duralast gold. Has been in the car for about 3 years with zero problems. Sent you a PM about pricing.

HeissRod