1991 300SL M-Benz Battery!!!

[spins23]

i just inherited a 1991 300SL M-Benz from my grandfather and i've got to jump start it all the time so how do you know if the battery is old and weak?

[G-Benz]

There is a inexpensive tool called a hydrometer (or something like that). Most auto parts stores carry it. Looks like a small turkey baster with a gauge.

You insert it into each of the battery cells and squeeze the bladder to obtain a sample of the electrolyte (water). The pH content measured by the device informs you of the state of the cell. One or more dead cells indicates that your battery is history.

Go to Interstate for a replacement. They carry the weird OEM size for a fraction of the dealer cost.

[Eli (NJ)]

Start the car and put a voltmeter across the battery terminals. If it reads around 14 volts steady, your battery is dead; if it's fluctuating up and down a few volts, then it's your charging system. Also, you can leave the meter on and shut off the car after a few minutes of running, if the voltage starts dropping rapidly over time, it's your battery again.

Remember, you don't want to keep jump starting this car, the electronic modules (especially the top's) don't like it.

Eli.

P.S. It doesn't hurt to check the battery terminals for corrosion first. This is the cheapest fix yet, just clean them.

[spinedoc]

Just grab a new battery, I was very pleased when I bought mine that it was only 100 bucks.

[Marc-1]

Get a new batt.....could be the whole problem with the little red button and the top not working as it works from the battery.....car running or not!!

[kip Foss]

Before you 'just grab a new battery', take this oppertunity to learn something about batteries. You can get a hydrometer at Wal-Mart or the like for about a dollar. Bigger ones (like a turley baster) are more accurate but you really don't need the accuracy and they break more easily.

Take your battery out of the car. Clean the battery clamps with a pointed wire brush battery terminal cleaner. Get one at the local parts house. Use the same tool to clean the battery terminals. Fill each cell with distilled water to the linit indicator. Leave the caps off the cells. Slow charge (6 to 8 amps) your battery over night. Put a section of newspaper under the battery. They bubble acid out when they charge. Check each cell with the hydrometer. The scale will tell you how well each cell is taking a charge. If one or more cells are not taking a charge your battery is basically rooted and you need a new one.

There are only about 4 battery manufacturers in the States so don't be confused by all the brand names. Check out Consumer Rreport magazine. Don't buy a battery with more CCA (cold cranking amps) than you need. More amps out of the same size case requires that the plates be closer together and therefore the plates will warp because of lack of cooling. I know from whence I speak.

Interstate and Die Hard batteries are as good as you will get. Varta's are very good but very expensive and I don't know that they last any longer. Don't get caught in the 'battery long life cycle guarentee scam'. You buy a battery with a 60 month guarentee and it goes belly up after 40 months. You take it back and they offer you $9-15 for the remaining 20 months. You figure, "Hell, I'm here and need a new battery and they will give me $10 towards a new battery", so you go for it. Now they sell you another crappy battery with another 60 month guarentee and in 40 months you are back again.

If you live where it is hot check your battery every month or so. Lack of water will kill the best battery money can buy. It doesn't hurt to put a trickle charger on the battery every once in a while and let it charge overnight esp. in you make a lot of short trips where the battery doesn't get fully recharged.

Read this item 2 times and give yourself credit for battery 101.