John E

Our 2013 S550 with 30,000 miles is on it’s second battery. The original battery lasted 3 years and was replaced in May, 2016. The replacement is a Duracell Direct fit AGM battery purchased from Batteries + Bulbs with a “48 Month Free Replacement Warranty”

Yesterday, my wife came in and said the car won’t start. Sure enough. Her car had been sitting idle for about a week. I put the charger on the battery and after 4 hours, the green light on the charger came on and all seemed fine. The car fired right up, I drove it to the car wash, filled up with gas and drove back home, about a 20-mile trip.

This morning I took the car to one of the local Batteries + Bulbs stores and told them my 3-year-old battery will not hold a charge for a full week. So, out comes the old gentleman with the battery tester. He hooked the tester to the terminals, set the cold cranking amps to 900 and switched on the tester. Within just a couple seconds, smoke cane billowing out of the battery. Not just a little smoke but a cloud, and not just out of the side vent hole but from all around the battery. The battery stopped smoking as soon as he turned the tester off. “I’ve never seen that happen in 30 years of working with batteries” said the old man. He went back and got the manager. “Must be something wrong with your car’s charging system, it held 900 amps, so the battery is fine. I’m no mechanic, so you need to have your car looked at by a professional”. says the manager.

After that fiasco, I didn’t know if the car would even start. Turns out it did and ran fine all the way home. When I got home, I researched “What causes a battery to smoke during a load test?”

Google offered a forum with two similar answers:

1. I'd say the battery is shorted internally. I've had 2 blow up here at the shop. One in the parking lot (hood shut) and one at my coolant flushing station.

The one at the coolant flushing station almost got me! I had just turned around to go get a tool when the whole top of it blew up and sent acid everywhere.

2. Internal short and reversal. Batteries do explode and lead acid will go into thermal runaway under charge.

I know I don’t want another load test and I know I don’t want that battery anymore.

I disconnected and removed the battery from under the hood. (That is one heavy battery.)

I set the battery outside the garage and tomorrow will put the battery in the back of my pickup and take it to the other local Batteries + Bulbs store (The store where I actually purchased the battery) and plead my case. I will warn them to take great care if they decide to perform a load test.

My theory is, our relatively light sometimes infrequent use, combined with all the electrical features on S550’s means a battery is only going to last about 3 years.

If anyone on this forum has any thoughts or insights, I would love to hear them.

Thanks!

dlafever

Cause and effect for me. If my battery is NOT smoking and you remove it and connect your tester and it starts smoking, your tester broke it and you owe me a battery.

Here in the desert 3 years is good battery life, 4+ and you are treading water. We see temps >100F for at least 60 days of the summer and heat kills batteries. I have found that batteries not located under the hood last longer in my Benzes (W210, R129, W221 Consumer battery which lasted 8 years!)

John E

That's just it. The test was performed with the battery in place and connected to the car's positive and negative mains! Seeing smoke pouring from the battery in the engine compartment with the battery connected is a horrifying experience.

I can only assume and hope connecting a load tester with the battery connected is a normal procedure and has not caused damage to our car's electrical system.

I agree, excessive heat shortens battery life. We're in Georgia, not the desert, nonetheless it's pretty hot here for a good portion of the year.

rustybear3

Take your battery in, get the pro-rated value and buy another battery. You got a bad battery. It happens.