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It has been mentioned many times before in the forum about battery drain on the 451 and how long can they sit without being untouched and still start up without the aid of a jump or a fresh battery. I had that problem with my Fortwo and I endeavored to get to the bottom of the battery drain issue with some cold hard numbers that we all could work from.
Now first let me say that anyone who knows me on the forum knows I am a dedicated tried and true gadget freak and there are many projects that I have inflicted upon my Fortwo, and each one was done with care and not just a cut and botch up kind of add on. I bought my Pure and shortly after having it and investigating all the options I could have had if I would have just bought a Passion or even the coveted Brabus, I decided to slowly add options to make it a full blown Passion clone. But that opens up some choices on the Fortwo due to it's configuration of electrcal devices. Since the Fortwo uses a Can Bus system to tie all the working electrical items together it can get tough doing all factory style upgrades like factory fog lights or factory heated seat option. Even if you were to find factory parts on E-bay or a donor car, plugging them up to the existing harness doesn't guarantee they will work when you flip the switch because many of the options has to be enabled or programmed into the SAM to power that item. For newbies the SAM stands for "signal acquisition and actuation module". It's just a fancy way of saying the fuse box with it's relays is controlled by a computer chip that controls how power is routed from the battery to the cars systems.
So I had the choice if I wanted heated seats. I could install either the seats themselves, find a button bank with the correct buttons, plug it all in, make a trip to my friendly neighborhood Smart Center to get it enabled through the SAM, or I could get on Ebay or Amazon and buy a heated seat kit and install it and then power it from one of the "R" terminals in the SAM and I was in business. Same deal for fog lights etc,...Well I added CREE LED fog lights, 5 way heated seats, LED's to more than mimic the Ambient lighting package, used a computer sound system, front and rear and internal DVR cameras, Android touch screen radio,....well you get the idea.
So the first thing to die was the original 2011 Smart battery. So after a quick survey of prices and batteries and their specs I figured out for me the cheapest battery was from Walmart and the specs weren't bad on it. So I installed the battery and was driving the car frequently and all was well in Graceland. Then when the weather got cold and bad I parked him in the warm garage and drove my daily driver. Well I soon learned after the car sat for a week or more the battery would be dead, and since the battery is buried under the passenger floor we know what a pain it is jump it or even get at it to connect a battery charger. So I opted for a battery tender and the first one I bought was rated for 500 miliamps at like 14 volts. So I plumbed that in and put my fortwo on an intravenous IV of power.
Well when the weekend came and I wanted to go for a spin, low and behold the battery was dead. Darn that battery tender. So I went and bought the largest tender I could find and it put out 750 milliamps at 14 volts and connected it up. The weekend came again and when I hopped in for a spin it was dead again. So I dug out my battery charger that was 2/6 amps and connected it the battery on 2 amps. Then I looked at the chargers gauge and it was reading about 1 1/2 amps. That's when I decided I needed to look in to parasitic battery drain. So I got out my multimeter plugged the leads into the proper jacks for a 20 amp test. I pulled the negatrive battery terminal and placed the meter leads in series with the battery post and the cable and viola I had a 1.25 amp draw. So I disconnected my new Android radio and it dropped down to 380 milliamps.
I knew from researching on the internet that I had to get it down to 50 milliamps or less to be in the neighborhood of newer cars. Alot of the newer cars use the can bus system of communicating because it is so much more efficient and I won't go into the particulars there, but newer cars have key FOBs and the cars computer sits and listens for the digital code from your FOB so it knows to unlock your door for you. You can imagine how busy the computer is at the mall parking lot or Walmart with all the different people locking and unlocking cars and all of those in range of your vehicle have to be listened to and sifted through as it listens for your FOB. Now the systems do go to sleep after a period of time depending on the car manufacturer. So the system draws a little power. The 451 listens for your key FOB to lock or unlock the doors. We have a clock in the dash that needs power to keep the correct time. If you have the dash pods, that clock is a crystal regulated clock with a stepper motor to advance the hands, so it needs power. If you have the optional car alarm it uses power when it's armed. If you have the auto lights on and auto wipers it needs power for a period of time after the car has been shut down before it nods off to sleep. So on astock Fortwo there is some battery drain and when you add gadgets like I have then it becomes too much for the little battery to cope with right? or is it?
Well when I discovered380 milliamps of drain I knew I had to charge up the battery. So with the terminal disconnected I pulled out my 10 amp battery charger and connected it directly to the battery while the battery was disconnected from the car. Well you may or may not know, if you have a completely stone dead battery and you hook up a battery charger to it the charger will usually read zero amps for a little while and then the charge rate will begin to climb slowly and after a couple of hours the charger shuld be charging near maximum and then as the battery stores the charge the charge rate will slow down until you are back to the 1 to 2 amp range again.
So I checked battery voltage and it was 9.8 volts and that's well below total discharge. So with the 10 amp charger on it it only showed about 1 amp of charging. So this was okay with me because of what I stated earlier about charging a totally dead battery. So I went upstairs to bed and I couldn't sleep for thinking about the situation. So after about 4 hours I went back downstairs and checked the charger expecting it to be on 10 amps of charging. Well it was still on 1 amp. I felt the battery case and it was warm. So that's when the situation became clear to me. I had a bad battery.
I let it charge the rest of the night and the next morning I disconnected the charger and let the battery set for about an hour for the charge to equalize between the cells and I checked battery voltage and it was 10.99 volts, so it was still dead and very warm to the touch. So I put it in the car and drove to Walmart and took the battery in to them and they said we have to charge it for an hour before we can load test it to see if it's bad or not. I told them it's been on charge all night and I just pulled it off charge. I told them to feel the case and they did, so they believed me. He load tested it and my 6 month old EverLast battery failed miserably.
So they gave me a new battery and I installed it in the car. I checked battery voltage and it was 12.6 volts which is very close to being fully charged. So without changing a thing or disconnecting a thing I did my battery drain test and instead of being 380 milliamps it was .005 amps. So the reading I got of 380 milliamps was because the battery voltage was so low the milliamps raised. So after 3 days I could wait no longer and I tried to start the car tonight and it fired up instantly.
So I was blaming all my gadgets and the last install was the new radio and I will admit at first I had it wired to power wrong. The Fortwo doesn't have an accessory position on the ignition switch, only OFF ON and START. To play the radio with the car sitting I would have had to keep the ignition switch on and I didn't want to do that. So I hooked the radio battery wire and accessorry wire(that keeps setting and the clock running) together on one of the SAM's R terminals that was hot all the time. Well the radio is Android and was going out on my WiFi and doing updates and things and using up the car's battery to do it.
So I did straighten pit the radio power wires sp it only plays when the key is on. Then I put a toggle switch between the radio battery wire and accesory wire so that if I want to listen to the radio with the key off I can flip the toggle switch on and do so. So with eveything hooked back up and that includes the radio and the MP5 player rear camera on my rear view mirror, battery drain went from 1/2 milliamp to 11 milliamps and that is well below the 50 milliamps that alot of newer cars have nowdays do to sophisticated electonics. And as for the systems on the Fortwo going to sleep, when you shut the car down and lock the door, watch for the backlight on the lower display (gas gauge, clock etc,..) to go out. You'll also hear a relay under the dash click and viola your systems are in minimal standby mode. So if you suspect it's the battery it could be, I sure found out the long way around. Sorry I wrote a book. Didn't mean to, but sometimes the difference is in the details.DCO
Now first let me say that anyone who knows me on the forum knows I am a dedicated tried and true gadget freak and there are many projects that I have inflicted upon my Fortwo, and each one was done with care and not just a cut and botch up kind of add on. I bought my Pure and shortly after having it and investigating all the options I could have had if I would have just bought a Passion or even the coveted Brabus, I decided to slowly add options to make it a full blown Passion clone. But that opens up some choices on the Fortwo due to it's configuration of electrcal devices. Since the Fortwo uses a Can Bus system to tie all the working electrical items together it can get tough doing all factory style upgrades like factory fog lights or factory heated seat option. Even if you were to find factory parts on E-bay or a donor car, plugging them up to the existing harness doesn't guarantee they will work when you flip the switch because many of the options has to be enabled or programmed into the SAM to power that item. For newbies the SAM stands for "signal acquisition and actuation module". It's just a fancy way of saying the fuse box with it's relays is controlled by a computer chip that controls how power is routed from the battery to the cars systems.
So I had the choice if I wanted heated seats. I could install either the seats themselves, find a button bank with the correct buttons, plug it all in, make a trip to my friendly neighborhood Smart Center to get it enabled through the SAM, or I could get on Ebay or Amazon and buy a heated seat kit and install it and then power it from one of the "R" terminals in the SAM and I was in business. Same deal for fog lights etc,...Well I added CREE LED fog lights, 5 way heated seats, LED's to more than mimic the Ambient lighting package, used a computer sound system, front and rear and internal DVR cameras, Android touch screen radio,....well you get the idea.
So the first thing to die was the original 2011 Smart battery. So after a quick survey of prices and batteries and their specs I figured out for me the cheapest battery was from Walmart and the specs weren't bad on it. So I installed the battery and was driving the car frequently and all was well in Graceland. Then when the weather got cold and bad I parked him in the warm garage and drove my daily driver. Well I soon learned after the car sat for a week or more the battery would be dead, and since the battery is buried under the passenger floor we know what a pain it is jump it or even get at it to connect a battery charger. So I opted for a battery tender and the first one I bought was rated for 500 miliamps at like 14 volts. So I plumbed that in and put my fortwo on an intravenous IV of power.
Well when the weekend came and I wanted to go for a spin, low and behold the battery was dead. Darn that battery tender. So I went and bought the largest tender I could find and it put out 750 milliamps at 14 volts and connected it up. The weekend came again and when I hopped in for a spin it was dead again. So I dug out my battery charger that was 2/6 amps and connected it the battery on 2 amps. Then I looked at the chargers gauge and it was reading about 1 1/2 amps. That's when I decided I needed to look in to parasitic battery drain. So I got out my multimeter plugged the leads into the proper jacks for a 20 amp test. I pulled the negatrive battery terminal and placed the meter leads in series with the battery post and the cable and viola I had a 1.25 amp draw. So I disconnected my new Android radio and it dropped down to 380 milliamps.
I knew from researching on the internet that I had to get it down to 50 milliamps or less to be in the neighborhood of newer cars. Alot of the newer cars use the can bus system of communicating because it is so much more efficient and I won't go into the particulars there, but newer cars have key FOBs and the cars computer sits and listens for the digital code from your FOB so it knows to unlock your door for you. You can imagine how busy the computer is at the mall parking lot or Walmart with all the different people locking and unlocking cars and all of those in range of your vehicle have to be listened to and sifted through as it listens for your FOB. Now the systems do go to sleep after a period of time depending on the car manufacturer. So the system draws a little power. The 451 listens for your key FOB to lock or unlock the doors. We have a clock in the dash that needs power to keep the correct time. If you have the dash pods, that clock is a crystal regulated clock with a stepper motor to advance the hands, so it needs power. If you have the optional car alarm it uses power when it's armed. If you have the auto lights on and auto wipers it needs power for a period of time after the car has been shut down before it nods off to sleep. So on astock Fortwo there is some battery drain and when you add gadgets like I have then it becomes too much for the little battery to cope with right? or is it?
Well when I discovered380 milliamps of drain I knew I had to charge up the battery. So with the terminal disconnected I pulled out my 10 amp battery charger and connected it directly to the battery while the battery was disconnected from the car. Well you may or may not know, if you have a completely stone dead battery and you hook up a battery charger to it the charger will usually read zero amps for a little while and then the charge rate will begin to climb slowly and after a couple of hours the charger shuld be charging near maximum and then as the battery stores the charge the charge rate will slow down until you are back to the 1 to 2 amp range again.
So I checked battery voltage and it was 9.8 volts and that's well below total discharge. So with the 10 amp charger on it it only showed about 1 amp of charging. So this was okay with me because of what I stated earlier about charging a totally dead battery. So I went upstairs to bed and I couldn't sleep for thinking about the situation. So after about 4 hours I went back downstairs and checked the charger expecting it to be on 10 amps of charging. Well it was still on 1 amp. I felt the battery case and it was warm. So that's when the situation became clear to me. I had a bad battery.
I let it charge the rest of the night and the next morning I disconnected the charger and let the battery set for about an hour for the charge to equalize between the cells and I checked battery voltage and it was 10.99 volts, so it was still dead and very warm to the touch. So I put it in the car and drove to Walmart and took the battery in to them and they said we have to charge it for an hour before we can load test it to see if it's bad or not. I told them it's been on charge all night and I just pulled it off charge. I told them to feel the case and they did, so they believed me. He load tested it and my 6 month old EverLast battery failed miserably.
So they gave me a new battery and I installed it in the car. I checked battery voltage and it was 12.6 volts which is very close to being fully charged. So without changing a thing or disconnecting a thing I did my battery drain test and instead of being 380 milliamps it was .005 amps. So the reading I got of 380 milliamps was because the battery voltage was so low the milliamps raised. So after 3 days I could wait no longer and I tried to start the car tonight and it fired up instantly.
So I was blaming all my gadgets and the last install was the new radio and I will admit at first I had it wired to power wrong. The Fortwo doesn't have an accessory position on the ignition switch, only OFF ON and START. To play the radio with the car sitting I would have had to keep the ignition switch on and I didn't want to do that. So I hooked the radio battery wire and accessorry wire(that keeps setting and the clock running) together on one of the SAM's R terminals that was hot all the time. Well the radio is Android and was going out on my WiFi and doing updates and things and using up the car's battery to do it.
So I did straighten pit the radio power wires sp it only plays when the key is on. Then I put a toggle switch between the radio battery wire and accesory wire so that if I want to listen to the radio with the key off I can flip the toggle switch on and do so. So with eveything hooked back up and that includes the radio and the MP5 player rear camera on my rear view mirror, battery drain went from 1/2 milliamp to 11 milliamps and that is well below the 50 milliamps that alot of newer cars have nowdays do to sophisticated electonics. And as for the systems on the Fortwo going to sleep, when you shut the car down and lock the door, watch for the backlight on the lower display (gas gauge, clock etc,..) to go out. You'll also hear a relay under the dash click and viola your systems are in minimal standby mode. So if you suspect it's the battery it could be, I sure found out the long way around. Sorry I wrote a book. Didn't mean to, but sometimes the difference is in the details.DCO
