Mercedes-Benz R230 Battery
From 2001 to 2011, the Mercedes-Benz R230 SL used a two-battery system. One smaller battery was mounted under the hood for engine starting. Another larger battery was mounted in the trunk for accessory use.
Because this car has a two-battery system, if you are changing either battery, make sure to disconnect the negative terminal of both batteries before working on either one, just to be safe (and reconnect terminals in the correct reverse order). We seem to see dozens of these R230s at auctions every year, from SL500s to SL55s with plenty of AMG versions. One very common denominator is low mileage. That confirms to us why Mercedes-Benz decided to install two batteries in the R230s.
These cars are packed with all kinds of demanding electrical accessories and components, including the retractable hardtop, hydraulic systems, AMC on many models, SBC braking on the earlier cars, COMAND, seat modules (a common source of parasitic draws), Keyless-Go, integrated alarm systems, a PSE pneumatic system, numerous SAM/control modules and a CAN network, just to name a few. Combine that high electrical demand with low mileage and you have a Mercedes-Benz that spends a lot of time sitting and discharging the battery.
As a result, we would recommend (and Mercedes does too), that you keep your R230 hooked up to a quality battery maintenance device whenever the car is parked at home, waiting to be used. There’s even a TSB recommendation for using a battery charger.
Which battery should you maintain? You can hook up two chargers to both batteries, but if the engine starting battery is properly isolated, it really shouldn’t have any issues and may only need to be checked a few times a year. If the voltage in the engine starting battery is at or above 12.6 volts, it’s fine. If it’s consistently below 12.4 volts, you may need to charge it more often and check to make sure there is no parasitic draw on that battery.
The more common culprit for battery woes is the trunk-mounted battery. When that battery gets deeply discharged, the car will still start, but you may see an “Electric consumers offline!” warning light when you turn on your heated seats or try to retract the roof. That means you should keep a quality battery maintainer on your trunk-mounted battery as it sits. That can get a little tricky if you forget it is plugged in and drive off with a maintainer dragging behind your car, so it wouldn’t be a bad idea to leave a reminder somewhere on your dashboard.
What About Lithium?
In terms of battery replacement, we sometimes hear R230 owners ask about lithium batteries. Many lithium battery brands do not offer engine starting batteries, but that is an option with OPTIMA’s lightweight QH6 ORANGETOP. At 21 pounds, OPTIMA’s QH6 lithium battery is about 33 pounds lighter than our DH6 YELLOWTOP. However, as that weight relates to an R230, it might only mean your SL600 now weighs 4,467 pounds instead of 4,500 pounds.
While OPTIMA’s QH6 ORANGETOP also offers vastly superior cycle life over any AGM battery, if you’re not using your R230 in a high-performance environment where there are many other weight-saving modifications being installed, like carbon fiber body panels, lighter wheels and seats, then the 33 pounds you save in a 4,500 pound car will probably not offer significantly noticeable performance gains.
The factory engine starting battery on the R230 is a 35AH battery, which is basically the size of the electrical fuel tank, while the trunk-mounted battery that powers the accessories has essentially double the capacity at 70AH of capacity. While OPTIMA’s QH6 ORANGETOP offers plenty of capacity for the engine starting battery with 45AH of capacity, that is obviously well short of the 70AH capacity of the trunk battery. OPTIMA’s DH6 YELLOWTOP exceeds the OE capacity with a rating of 72AH.
However, lithium batteries are far more efficient in their operation, so you may get up to 90% or more of the rated capacity out of a lithium battery without any issues, whereas an AGM lead-acid battery will start to see significant declines in cycle life when they are regularly discharged below 50% state of charge, so the capacity difference for lithium may not be that significant.
OPTIMA’s QH6 ORANGETOP also has a built-in CPR system that will automatically disconnect your battery from a current draw if it is being deeply discharged, holding enough energy in reserve to start your engine one more time.
The bottom line for many R230 owners, regardless of the battery technology they choose, is proper voltage maintenance. We’re so confident this will maximize the performance and lifespan of your battery, if you purchase an OPTIMA battery from us and buy an OPTIMA D1200+ battery charger at the same time, we’ll add an additional year of free replacement warranty coverage to your OPTIMA battery.
