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After observing battery voltage gauge on my car, I can see my lead acid battery operate voltage is from 11.8v to 14.8v.

The car is about 5 years old, and while start/stop, the car drains the lead acid battery, and voltage drops from 14.8v immediately to 12v and when it drops to ~12.2v, the engine ignites again. the stop won't last more than 30 seconds, which is annoying.

Now I would like to have a new battery that prolongs the start/stop time.

I intend to use Panasonic NCR18650B Batteries. 3 in series many in parallel. lithium ion packs with BMS battery management system.

But charging will easily pass 4.2v for each cell. 14.8/3=4.93v, when discharging, batteries is ok: 11.8/3=3.93v.

If I use 4 in series, 14.8/4 = 3.7v and 11.8/4 = 2.95v. And batteries will only be partially charged to 3.6~3.7v, which is another problem. and might get over discharged.

Any suggestion for me to use these NCR18650B to replace the traditional car batteries?

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    \$\begingroup\$ Planning on setting fire to your car ... ? \$\endgroup\$ – brhans Dec 2 '16 at 1:51
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    \$\begingroup\$ I think you have some shorted diodes on 3 phases , there are 6 diodes and if Vbat after full charge drops below 12.5 there is a bad cell. Loose contacts and fan belt prevent correct operation too. A 650A CCA LiPo array and regulator is expensive \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Dec 2 '16 at 2:00
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    \$\begingroup\$ @brhans not fire, but innovations \$\endgroup\$ – c2h2 Dec 2 '16 at 2:14
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    \$\begingroup\$ The basic premise of this "question"(?) borders on the insane. If there is a problem with the charging circuit, then it is likely a simple matter to fix quite economically. Engineering a $1000+ exotic solution to a common vehicle electrics problem is just silly. \$\endgroup\$ – Richard Crowley Dec 2 '16 at 4:35
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Your car provides a amp draw of 100+ while on, headlights, fan. Those 18650 cells are not even going to last a minute.

If your car is dropping to 12V at a stop light, then you have alternator system issues. A loose cable, alternator belt, bad battery, something. A five year old car should not be experiencing such issues yet. Fix the underlying problem instead of trying to bandaid a hole in the titanic.

Edit: Of course if you are trying to build a proper Lithium equivalent battery, 600+ Cold Cranking Amps capable, it still won't work properly if you try to run the car on it without a working alternator. The Alternator or Generator powers the car while on, the Battery is mainly for starting the car.

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  • \$\begingroup\$ 250F super cap + lithium batteries for handling 600A issue and 100x 18650 batteries, makes 3.4Ah * 3.7v * 100 = 1258Wh or 12v 100Ah \$\endgroup\$ – c2h2 Dec 2 '16 at 2:16
  • \$\begingroup\$ please read: jalopnik.com/5527441/porsches-new-1700-car-battery-what-you-get \$\endgroup\$ – c2h2 Dec 2 '16 at 2:20
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    \$\begingroup\$ I too, think this is a band-aid to the real problem - probably a faulty alternator. But all those lithium-ion batteries, in the summer, in a hot engine compartment, with the vibration, are going to be a fire/explosion waiting to happen. In the winter they will die below freezing. Try it if you must, but I'd suggest carrying a fire extinguisher in the car. \$\endgroup\$ – rdtsc Dec 2 '16 at 2:55
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    \$\begingroup\$ @c2h2 No offense, but do you think your home made battery will be equivalent to a Porsche battery? They most likely have a team of people working on this (that do this kind of thing for a living). \$\endgroup\$ – Tyler Dec 2 '16 at 3:50

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