How to keep a mild hybrid charged?

[KISS_ME]

Hoping someone can help shed some light on how to keep a mild hybrid charged if i leave it for extended periods of time.

I understand the E53 use a 48V system paired with a starter generator to crank over the vehicle. If the 48V battery is drained i would assume car wont be starting? Generally i've used a trickle charger in the past if i'm not using car but my understanding is that only charges the 12V system. does anyone by chance know if the vehicle has a step up mechanism to charge the 48V system using the 12V system if i keep it topped up with a trickle charger? i've tried calling all 3 MB dealerships in Calgary to get this answered and nobody seems to know.

assuming worse case scenario and i can't keep the 48V topped up does anyone know if these vehicles can be jumped? just doesn't make sense to me that a 12V battery can jump start a 48V battery? the manual provides instructions to do it but im not sure if its for the non-hybrid version.

[ShermanEF9]

From how I have understood it, the high and low voltage systems in almost all EV/HEVs are separate.

[killramos]

The battery on a mild hybrid will basically never die.

Best you can do is just drive it, I’ve seen lots of conflicting info that you shouldn’t even trickle charge them on the 12V posts at least for BMW’s.

[rage2]

Something I can answer correctly haha. First, to answer your questions directly, then I'll explain the system.

Trickle charging the 12V battery will very very slowly charge the 48V battery. It's buried in the manual. Like killramos says, the 48V should never die. Now the long explanation.

Car has 2 circuits, 12V for all your basic accessories, and 48V for things that are only used when car is on (AC, water pump, oil pump, ISG starter/motor/generator, e-turbo, airmatic pump, etc). When the car is off, the 48V is never drawn so it shouldn't go down, which also means it'll never charge the 12V battery. The 12V battery is the easiest one to die on this car. I've had it complain of low battery from wrapping the car for a week without the car being started since it turns on lights and other crap.

The car also ensures the battery never dips below a certain amount (I'm guessing 50% or so?) and if it does while driving say at a track, it stops providing ISG and e-turbo boost to stop draining battery, and goes into aggressive charging mode. You basically have a really laggy car at that point. In the winter, I've had my car parked in -30C outside for a day, which would kill battery capacity, and once it's started prior to battery warming up, there was no e-boost and same thing happened.

The car charges the battery as much as possible from braking, cruising, and idling. If the battery dips below a certain point like above example, it will also draw drive energy while driving (ie cruising on highway) to charge the battery. It does everything possible to ensure the battery never dips below that certain point.

Now, what happens when you park it for an extended period of time? The 48V battery is never used when car is off so it should never drain. Only time it loses energy is in extreme cold like I mentioned earlier, and even then there's more than enough capacity to start the car. If for some reason the battery is critical (both 12V or 48V) the car alerts you on Mercedes Me and email to start the car immediately to charge it up. You get a ton of warnings. And as mentioned originally, if the 48V is low and for whatever reason you don't want to start it up to charge it, a trickle charger on the 12V circuit will very slowly charge the 48V battery. No clue how long it takes. As for how long you can park it, I've had my E53 coupe parked all summer, something like 2 months before I got warned on 12V battery.

Hope that helps.

[KISS_ME]

Awesome write up! huge thanks for the explanation!

Any inputs on keeping these after a lease? not sure if i want to deal with the hassle of owning such a complex vehicle but at the same Last time i went to a dealership i was given a napkin quote of $120K for a new E53 and $80k for a RDX. The dealer mark ups are getting pretty stupid lately.

[rage2]

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Awesome write up! huge thanks for the explanation!

Any inputs on keeping these after a lease? not sure if i want to deal with the hassle of owning such a complex vehicle but at the same Last time i went to a dealership i was given a napkin quote of $120K for a new E53 and $80k for a RDX. The dealer mark ups are getting pretty stupid lately.

I’m planning on keeping mine and buying extended warranty on it, unless the CLE63 cabriolet works for me in terms of space and not asking crack money for it. It’s a roll of the dice. I think the 48v battery is a 10k replacement expense. At some point it’ll die depending how long you’re keeping the car. Same goes for the air suspension at around 160k kms.

[Flexray]

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Hoping someone can help shed some light on how to keep a mild hybrid charged if i leave it for extended periods of time.

I understand the E53 use a 48V system paired with a starter generator to crank over the vehicle. If the 48V battery is drained i would assume car wont be starting? Generally i've used a trickle charger in the past if i'm not using car but my understanding is that only charges the 12V system. does anyone by chance know if the vehicle has a step up mechanism to charge the 48V system using the 12V system if i keep it topped up with a trickle charger? i've tried calling all 3 MB dealerships in Calgary to get this answered and nobody seems to know.

assuming worse case scenario and i can't keep the 48V topped up does anyone know if these vehicles can be jumped? just doesn't make sense to me that a 12V battery can jump start a 48V battery? the manual provides instructions to do it but im not sure if its for the non-hybrid version.

The 12v system charges the 48v system. The car has a dc/dc converter, it is basically a big step up/step down transformer. It takes 12v power converts it to 48v, it can also take the 48v and turn it into 12v. The vehicle will move power though both systems to where it is needed.

[ExtraSlow]

Anyone have insight into typical parastic draw during storage in one of these systems? Must be higher than ice vehicle, just with how many persistent systems are active.
Probably not higher than the smallest battery maintainer, but interesting to think about.

[Flexray]

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Anyone have insight into typical parastic draw during storage in one of these systems? Must be higher than ice vehicle, just with how many persistent systems are active.
Probably not higher than the smallest battery maintainer, but interesting to think about.

The high voltage systems are isolated when the vehicle is shut off (48v to 900v). The HV is used mostly just to move the vehicle, most systems take the stored hv dc, and convert it to 3 phase ac that the drive motors use.

The 12v system runs the control side of things, all of the control modules, communication networks, convenience systems, lighting, etc. Parasitic draw goes up when modules have to be kept alive to hold memory, or when the vehicle checks in with its manufacturer (telematics). The 12v system is not a whole lot different on ICE compared to EV/hybrid. Some manufacturers publish parasitic draw specs, some don't. Most vehicles are in the 15 to 30mA range.