Battery Life in the Winter - Removing and Recharging an R129 Battery

As everyone knows, to keep the car battery charged, you need to drive it regularly. With an R129 Mercedes, it's more likely than not that you won't be using it as your daily driver, which is also the case with us. Our daily driver is the train and we are also lucky (or unlucky, as you may choose think when you read on) to live in an area where the train station, restaurants and supermarket are all within walking distance. So the SL500 is purely a go to the cinema on the weekend / day trip to the coast kind of vehicle.  

In summer, it's easy to pick a destination for a day trip as the weather is generally very encouraging for exploration. Winter, however, is a wholly different matter - it's cold and dark and a day at the seaside really doesn't sound very inviting. So while the car was standing outside in the cold and wet, we were trying and failing to find a convincing reason for a long enough drive to charge up the battery. 

Unsurprisingly, one day, when we decided to venture out to a shopping centre, the car wouldn't start. We briefly considered jump starting, but our jump starting device was even more dead than the battery, so that was that. There are also opinions that jump starting can damage the electrics on the R129 (which may or may not be true).

So we decided to take the battery out, buy a charger and charge it up at home. I found a great guide on how to disconnect the battery, so rather that trying to invent the bicycle, I will just direct you here to read it. What I will offer in this post though is our observations on the process. 

First of all, it's extremely fiddly. There are cables located right by the terminals (why???), the space is very tight (again, why???), you can't really see what you're doing, and it's difficult to got enough leverage to push properly. Secondly, make sure you have a long enough extension before you start - we didn't, so even after undoing the fastenings on the terminals, we couldn't get the battery out as it was also screwed on to the bottom of the boot. Finally, the battery is HEAVY. If you need to carry it for a while to get home, you will either need to stop and rest or perhaps get someone to help.

Now for the charger. Considering the whole battery (we have a Bosch S3) is worth around £100 pounds, we thought a cheap and cheerful charger would do the job, so off we went to the local 'we sell everything but not necessarily of very good quality' corner shop to get one. Up until this moment, we lived in blissful unawareness that there are different chargers depending on how big your battery is. So it was quite a surprise to be asked about the size of our engine. Of the two the shop had, we did get the more powerful one, but it was a no name brand, which became even more evident when the package was opened at home.

The charger emitted a disgusting plasticky stench, which became even worse once we connected it to the battery and switched on. The smell was so bad we had to open the windows everywhere. After a while, it got even worse and started to smell of burning plastic and all the lights on the charger went out. That was the end of the cheap and, as it turned out, not so cheerful charger.

We decided not to get a replacement but go to Argos and buy a different brand. Found an RAC 12V automatic charger for £50, which had good reviews and promised to be suitable for batteries up to 180Ah. It was heavy and solid, made of metal, didn't smell nasty on opening, which was a good sign, nor did it smell while charging. 

As you can see on the photo, there is an analogue display where you can see how many amps the battery is drawing and also how full it is - the emptier the battery, the more amps it will be drawing. The RAC charger did the job very well and we were soon in possession of a full battery.

Finally, some advise on reconnection. Once you reconnect the battery, the car alarm will reset and go off because you have the boot lid open. Have the remote ready to unlock the car - that will stop the alarm. Also, given how tight and fiddly the terminal fastenings were, we were tempted to just clasp them on and not tighten the fasteners. Unfortunately, that was not a stable option as the movement of getting into the car was enough to disrupt the contact and disconnect the battery. So we had to get right out and tighten everything properly.