Maintaining your Mercedes Battery

Slow Charge/Floating your MB Battery
As was described in the previous section re 'reconditioning' or 'equalizing' your MB battery, this section details the "maintainance" techniques that will guarantee a fresh battery even if the car sits for long periods without being started or run. This is a regular occurance now b/c I don't use the car as much as I did. I ride my bike instead!!

Recently, I removed my old Alpine GPS system in favor of a newer, more compact system made by Navigon, Model 7100. This was gift from my son who purchased it and found that he didn't need it. A very nice gift and very much appreciated. My old Alpine read the master map CD located in the trunk. Of course, this is much slower than today's methods [read a flash memory chip] so route calculation typically took up to 3 minutes. The Navigon takes 30 secs. Also when a route is changed on-the-fly, the Alpine would take up to 2 minutes to recalculate the new route whereas the Navigon takes 5 secs or so.

Unlike the Alpine that didn't have an internal battery, the Navigon does [Li_Ion] and it requires apx 5V @ 1amp of charging current whether it is "on" or in "standby" modes. So keeping the Navigon's battery charged will ultimately cause the car's battery to discharge especially when the car experiences long periods of inactivity. So some form of charger is needed b/c charging the car's battery will also charge the Navigon's.

After doing some Internet reading, I purchased a small battery charger/maintainer made by Schumacher, Model 1562A. There are a number of similiar models under this part number but they're all about the same. The price varies quite abit so shop around. The best price I found was at Walmart for $20.22.

It features microprocessor control with automatic voltage detection (6V or 12V). It has a multi-stage charging algorithm and desulfation along with a "Maintain Mode". It is also temperature compensated which prevents the battery from overheating. It displays the power and charging status and it works for small or large capacity batteries. It has a versatile quick connect harness that easily changes between battery clamps or ring terminals. It's also features reverse and short circuit protection.

The main operating controls are shown to the right: after making connection to the battery, the microproccessor will take the battery through a 'charging' state, up to 14.8V. Once it's properly charged, the unit switches to a 'float' charge mode where apx 13.3V is applied. If the current demand changes, the unit will go back to a charging mode until the battery is charged, then reverting to the float mode. All-in-all, a simple, straightforward battery maintainer system for a really decent price.


I used the so-called "Ring Terminal" battery connection and these were permanently attached to the battey with the provided cable. To charge or maintain the battery, all that is needed is plug in the quick-disconnect cable and turn the charger on. This is very handy for maintaining the battery wihout having to directly access the battey compartment. On the W140, it's next to the spare tire on the right rear side of the car in trunk under the carpet. The connecting cable shown in the picture is apx 10' in length and has a mating quick-connect apx in the middle. When not in use, it stores nicely in the trunk.




Charging times vary depending on the size of the battery (amphours) and the state of charge. The table shows the typical charging times based on various battery sizes. A MB battery for the C140 (or W140) is typically 500 CCA mimimum with the one I have around 750 CCA capability. From the table, that shows that it could take from 19-1/2 to over 24 hours. Initially, my battery required about 17 hours when first connected to the Schumacher. Now it takes about 2 - 3 hours to attain the float mode.

Definitely a worthwhile purchase to ensure that your battery is at peak condition even if it sits for long periods of inactivity.

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