DIY Low Voltage Lithium Booster Pack

From what I have read so far the newer cars equipped with a low voltage lithium battery will not boost from a standard 12v booster pack simply because the voltage is too low. The Tesla lithium consists of a 4S setup which is around 16.4v. There is a little more to it however after all the electronics inside the new battery are done with dealing with the output it falls to around 15.5v.

When the tow service shows up and magically boosts the car with his magic booster it is really only another 4s pack capable of higher voltage.

I have a few RC toys and therefor am familiar with lithium packs. I made my own compact booster packs several years ago which will put anything on the market designed for boosting to shame. I did choose to use 4s at the time as I figured a bit more voltage for boosting purposes is a plus. Have a few of these I keep in both cars and on the boat. Have used them more than once to help a stranded car owners in need of a boost, snowmobile, PWC, lawn tractor and have even used it as a 12v power supply for odds and ends such as an inflator and even a 12v transfer pump. Point is they are very useful in many applications.

When your low voltage battery on a Tesla goes too low you may not be able drive it or even get into it. Boosting will possibly solve both or at least get you into the car. This video explains it but shows the older convention lead acid battery where any standard booster pack will work. Again, standard booster packs do not work on a lithium battery equipped Tesla as they output only 12v where 15+ is required. This booster pack will also work on standard lead acid batteries therefor the best of both worlds.

A set of compact booster cables, some EC5 soldered connectors and you have a booster pack. Everything to make one is available on Amazon for those that may want to make their own.

CAUTION, there is no safety on these home made units meaning it will short if the 2 clamps touch and there is a rather large amount of dangerous juice available in them, actually can easily be even more than the Tesla lithium pack which is only 6.9AH! In my case it is 6.5AH so pretty much equivalent to the Tesla battery. Battery is only 5.5" long. There is also no reverse polarity protection so it you hook this up incorrectly to the battery you will be welding something!

There are clamps available that will protect against reverse polarity or short circuit however I have no tried them so cannot say if they work well or not.

 

[bfayer62]

Nothing wrong with your solution, but without reverse polarity protection, as you say caution is needed, and could result in damage to a lot of expensive components. Having said that a lot of inexpensive boost packs don't have reverse polarity protection, and can do the same damage.

A standard "2 volt" boost pack will start a Tesla with the new lithium low voltage battery. Yes the system runs at 15.5v, but 12.5 will boot the car up and operate just fine.

My NOCO boost pack puts out 14+ volts, which is more than enough. It may drop to 12 volts with a 1000 amp draw when starting an ICE vehicle, but not when booting a Tesla. All it needs to do is boot the system and unlock the doors..

 

[Midnightsun]

Maybe you can get the doors to unlock and such with a standard boost pack however this article will put more light into what I was referring to regarding putting juice back into the low voltage Lithium Tesla battery.

 

[Midnightsun]

My NOCO boost pack puts out 14+ volts, which is more than enough. It may drop to 12 volts with a 1000 amp draw when starting an ICE vehicle, but not when booting a Tesla. All it needs to do is boot the system and unlock the doors..

Don't think so because dissembling a NOCO unit several years back is what prompted me to make my own after I saw what a tiny battery they use. NOCO uses a 3S battery which is rated at 11.1v however fully charged it is capable of 12.6v. Here you can see what a little battery there is inside if you go to 2:45 of the clip and watch for a minute. (not me by the way) Granted this is their GB40 which is only 1 up from the smallest they offer. I do have a GB150 which has lots of power however 12.5v if tested with a voltmeter, no more. Again, 3S battery.

Not dissing NOCO in any way, their units are very nice and well made, just a little annoyed paying so much money for the tiny battery in their unit worth about 15$ at most. I did have the same GB40 unit as in the video by the way, bought several as stocking stuffers for the kids when they first came out, lasted about 3 years and then they were dead so I disassembled one out of curiosity.

 

[hmadsen]

I would imagine that if the battery was "flat" a normal 12V booster pack would probably be enough to get the computer running long enough for the car to boot up and start up the HV battery charger to charge the lithium battery.

The increase in voltage has more to do with the chemistry and resulting battery voltage, than it has to do with "needs to be higher voltage". I bet there is a buck converter installed to make the 15 volt into 12 volt for the different "computers" inside of the Tesla

 

[Wattsisname]

Maybe you can get the doors to unlock and such with a standard boost pack however this article will put more light into what I was referring to regarding putting juice back into the low voltage Lithium Tesla battery.

Help! Under what circumstances is an 8 month old Lithium battery likely to run out of juice? Would this be because the high voltage battery is to low to "feed" the Li-Ion ?
I had imagined a couple of years without having to worry about it.

 

[hmadsen]

Help! Under what circumstances is an 8 month old Lithium battery likely to run out of juice? Would this be because the high voltage battery is to low to "feed" the Li-Ion ?
I had imagined a couple of years without having to worry about it.

I would imagine that leaving a Tesla powered down (Locked doors, etc) would drain the battery, as all of the electronics are run off of that in, not that long of a time.

I can not imagine the low volt battery, needing very much power from the HV battery to charge. Somewhere in the "less than 1% from flat to full".

I dont know if a Tesla will wake up and charge the low voltage battery, if it detects it gets "low" even if the car is "off"

 

[Midnightsun]

Help! Under what circumstances is an 8 month old Lithium battery likely to run out of juice? Would this be because the high voltage battery is to low to "feed" the Li-Ion ?
I had imagined a couple of years without having to worry about it.

Mine did with 76% left in the high voltage battery. Car is 13 months old, problem was a harness connector that needed to be cleaned so I must assume it was never properly seated from the get go. Reason I keep these packs in my cars is mostly to help ICE vehicles in winter time if I can lend a hand. Did not think I would need it myself. Technically they should last for many years without issue and if it does start going bad you will get a notice saying you should have it serviced well before it completely gives up. By the way, the Tesla lithium low voltage battery is very tiny, only 6.9ah which is about the same size as an backup battery for an alarm system. Heck my wave runner battery is 20AH. so about 1/3 the size of that. Did I say tiny?

 

[CaliCowboy]

Lol this is very cool that you were able to achieve this yourself but I'm not confident in my abilities

 

[Wattsisname]

I would imagine that leaving a Tesla powered down (Locked doors, etc) would drain the battery, as all of the electronics are run off of that in, not that long of a time.

I can not imagine the low volt battery, needing very much power from the HV battery to charge. Somewhere in the "less than 1% from flat to full".

I dont know if a Tesla will wake up and charge the low voltage battery, if it detects it gets "low" even if the car is "off"

 

[jcanoe]

I dont know if a Tesla will wake up and charge the low voltage battery, if it detects it gets "low" even if the car is "off"

Yes it will. If estimates are correct then the Tesla Model Y draws ~25W when in sleep mode for the vehicle alarm system (not Sentry mode), door locks, LTE and BT modems, NFC. The 15V, 6.9 Ah lithium starting battery can be more deeply discharged than the older 12V lead-acid battery could be discharged.

Ohm's Law yields 25W/15V = 1.6A draw. Assuming a 90% discharge the 6.9Ah battery would need to be recharged every ~4 hours when the Tesla Model Y is in Sleep mode. When the Tesla Model Y is in Standby mode as when Sentry mode is active the power draw is ~230W. This power comes from the high voltage battery and the Tesla Model Y's power conversion system (PCS). The PCS is capable of delivering up to 2kW and also maintains the 15V starting battery. Estimating the charging amperage for the lithium starting battery between 5 amp and 10 amp this would require between 30 minutes and 1 hour.

 

[evrepair]

The car will boot up when powered from approximately 12V and up. Standard voltage for maintainers at Tesla service centers I believe is 13.5V. If contactors close, disconnect the power source - the car should support itself now. If contactors stay open, disconnect the LV battery to avoid draining it if you want to continue to power the car from external source.

 

[MakeSaveInc]

Mine did with 76% left in the high voltage battery. Car is 13 months old, problem was a harness connector that needed to be cleaned so I must assume it was never properly seated from the get go. Reason I keep these packs in my cars is mostly to help ICE vehicles in winter time if I can lend a hand. Did not think I would need it myself. Technically they should last for many years without issue and if it does start going bad you will get a notice saying you should have it serviced well before it completely gives up. By the way, the Tesla lithium low voltage battery is very tiny, only 6.9ah which is about the same size as an backup battery for an alarm system. Heck my wave runner battery is 20AH. so about 1/3 the size of that. Did I say tiny?

Thanks for telling. So If I make a lithium bank: 4s = 4.2v x 4 = 16v with 8 amp. should work? replace my model Y 2021 battery?. I saw the young guy and 3 girls in 20s. in Model X struck in freeway 5 north to San Francisco in Dark night middle of no where (12v dead). Very scary. I was with them until tow truck came. I also thinking about build 4s Lifepo4 but since you guys said it charge at 15.5v I think this would make the pack shut off. 3.65v max for lifepo4. But if the 4.2v x 4 in this case is an ideal but both pro and con. ....

 

[evrepair]

Don't build a custom lithium battery (many reasons why), if you are worried about your lead acid dying, just replace it every 2 years with an OEM one that costs $85.