Dead Battery - time to trade her in?
 

Second time now - battery totally dead.

Wife left lights on the first time and this time who knows?

Is it time to trade her in? Any suggestions?

1993 190e 2.6

I always trade in my car when the battery goes bad. Lot cheaper than trading in a spouse.

Sereiously, although it's nice to know the model and year of your car it's important to know the age of the battery. Since you did not state this i can only assume the battery is original which would be incredible (10 years!). Generally I replace a battery after 5 years when i have the first hints of potential failure. If you accidentally drained it completely several times the life of the battery is seriously compromised. DOD (depth of disharge) has a huge impact on battery life, I would say that the depth of the discharge is more important in defining battery life than the number of dicharge/charge cycles it's been through. BTW, if you have maintenance battery make sure you cover the plates with water. Distilled water is the best but drinking water is better than nothing if you notice through the fill holes that the plates are getting exposed.

That said batteries are electrochemical devices and as such are rather complex to characterize from any single or even several variables. Operating/storage temp, charging circuitry, depth of disharge (typically measured in amp-hrs), charge and disharge rate (measured in amps), number of charge/discharge cycle life... will result in very different outcomes for "identical" batteries. For example a lead acid battery that rearely gets deeply discharghed (including from self discharge) and stays "topped off" will last longer than one that gets deeply discharged.

I believe every home mechanic should have a trickle charger which can be left on the battery over night when needeed. They are cheap and allow you to charge up a deeply discharged battery. Counting on the alternator to do it after a jump start is not enough unless you are driving a lot of miles after the jump. A little 4 amp or less charger is real cheap and reduces the chance of overcharging if left on too long.

I have an 88 with over twice your milage and I just bought a new Optima battery. Batteries are cheaper buying a new car. I'll think about replacing it at 300K.

Their is an item that you can get that will only let the battery discharge so low, and it still can start the car. It attaches to the battery. Good cure for people who forget to turn off the lights.

Once a battery's been drained totally flat, my experience is that you'll either replace it immediately, by choice, or within two weeks or so, by necessity. If' the lights were left on, there may be a little life left; if you ran it too dry, it's a boat anchor now.

You need a way to measure the state of charge. A hydrometer is best, but can only be used on a non-sealed battery; a simple Radio Shack voltmeter works on all of them--if you don't have one, get one. With some drain on the battery (eg headlights) you should see at least 12.6 volts at full charge, about 12.2 at 50%, and if it's 12.0 or less you're flat. Under normal circumstances, your battery should never be as low as 50%.

I've never had a charging system fail, but I've replaced several batteries. A few have been run flat by error, but more often they've gone flat from lack of water. Use distilled if you can, reverse-osmosis "purified" otherwise. Avoid tap water except in dire emergency; it's better to drive a mile or two to a store than add the minerals and chlorine of tap water to the cells.

Trade in a wonderful car because the battery is due for replacement? Did I read your post correctly, Paul? Are you serious?

And my friends used to accuse me of trading in cars because the ashtrays were full (before I got my MB) ...

Seriously, if this happens again, and you don't have time or transportation to buy a battery, you can always call 1-800-FOR MERC 24/7 and they'll send out a mechanic and a nice, fresh battery (and only charge you for the battery, I believe).

I think he was refering to her not his car.

Killing a battery TWICE is definitely going to shorten it's life, but it's tough to say by how much. Since I use the same battery in both my 190 and MR2 (swap the cars and battery back and forth, 190 is "winter car", MR2 is "summer car"), I found that a Group 26R works fine as a replacement for the Gr. 47 in the Merc and Gr. 35 in the Deuce. Autozone sells 26Rs for 39.95. They are made by Johnson controls - same as the batteries at Pep Boys and Costco - just different labels, and have a 60 month warranty. I remove the labels and end up with a "plain black battery". For my conditions, these batteries typically last 7-8 years (if I don't severely discharge them), but they rarely see cold weather.

Duke

NOW I get it! ;)

If it's not the BATTERY you were asking for suggestions about--you're on your own, man!

I don't let the situation degrade as far as a bad battery before I trade. I trade when the tire pressure gets low.

Doesn't your car buzz when the lights are left on?

Perhaps she just needs a hearing aid. Would be a shame to give up a perfectly good wife that just needs a minor repair...

But seriously folks...
If there is no way to retrain her, you may want to consider one of those "Battery Buddy" thingies that cuts out when voltage drops to a critical breakpoint.
An alpha-geek could wire up a timer, and some relays, such that the lights would automatically turn off, say 5 minutes after the ignition was cut, just like many modern cars do.

Spiral cell batteries, such as the Optima, are said to be immune from damage from a deep discharge.

My Saabs had the headlights wired through the ignition so that parking lights were available with key off but headlights weren't. Shouldn't be a huge problem to achieve on an MB (or is it?)

That would be even easier. Just some relays with no timer.
Though, even the parking lights would drain the battery overnight...

Send a picture.. Is she "high milage" ???:D