# Car starter (dead battery) Lithium battery power bank

#### lumen aeternum

##### Enlightened
29.6 Watt Hours divided by 11.1 (3S nominal Volts) = 2.666 Amp Hours. It does not appear to be anywhere near 7500 mah. I have found that many add the number of cells in Serial and also add the number of cells in Parallel when the pack is only 1P. It looks like that's what they have done here.
So the 7500 mAh is a bald faced lie?
Is there some way of adding things up that gets that result?

W = A x V so

The 29.6 Watt hours is the total of 12 cells at 2.7 volts?
Nee to series stack 3 cells to get desired voltage,
therefore 12/3 = 4 parallel stacks, so 29.6/4 = 7.4 Ahr = 7400 Mah ?

Doing it another way gives me a different answer, but I gotta go to bed.
I always end up trying to do this stuff when exhausted.

? The pack is three batteries in parallel,
where each battery is a series stack of
3 x 2.7 volt cells, so outputs 11.1 volts.
And 3 x 889 mAH cells = 2.66 Ah for the stack?

So 3 x 2.66 Ah in parallel = nearly 8 Amps at 11.1 volts steady, and something more instant?

Don't understand "when the pack is only 1P."

On the label, is 40C a charge rate, or the temperature at which the pack was rated?

#### Poppy

##### Flashaholic
CPF Supporter
29.6 Watt Hours divided by 11.1 (3S nominal Volts) = 2.666 Amp Hours. It does not appear to be anywhere near 7500 mah. I have found that many add the number of cells in Serial and also add the number of cells in Parallel when the pack is only 1P. It looks like that's what they have done here.
So the 7500 mAh is a bald faced lie?
Is there some way of adding things up that gets that result?
----------------------------------------------------------------------

No it is not a bald faced lie.
As BVH already said, it appears that they added the watt hours of each of the 3 cells within the pack.
Let's try the math another way:
3S means there are three cells
so if we divide the total of the battery pack by three
each cell has 29.6/3 watt hours = 9.86 watt hours

now... V x A = watts
V x Ah = watts h
lets substitute 3.7 volts each, then

3.7 V x Ah = 9.86 watt hours
now we divide both sides by voltage
Ah = 9.86 watt hours / 3.7 V

Ah = 2.66 for each of three cells, so if you add them up...
3 x 2.66 Ah = 7.8 Ah or 7800 mAh

#### BVH

##### Flashaholic
Supporter
If you have only 3 cells total and it's a 3 In-Series configuration for 11.1 Volts nominal, then you add cell Voltages but do not add cell Ah since there's none in Parallel. So it's a 2660 mAh pack. Yes, they are not telling the truth.

Edit Add: After I re-read your post above I have the following question. How many cells make up the pack and how are they configured? If you have 3 stacks of 3 - 9 cells, then it might actually be the 7800 mAh pack claimed. I was thinking there were only 3 cells total.

#### Poppy

##### Flashaholic
CPF Supporter
Honestly I don't know how many cells make up that pack. It is a rectangular cube? I didn't examine it closely, but there weren't any obvious demarcations of individual cells wrapped in plastic.

So yeah, it appears that they are being deceptive in labeling it a 12V battery and 8,000 mAh

#### BVH

##### Flashaholic
Supporter
This has been my experience with Anti-Gravity microstart units. But in the end, they start the vehicles and that's why we buy them.

#### turbodog

##### Flashlight Enthusiast
Honestly I don't know how many cells make up that pack. It is a rectangular cube? I didn't examine it closely, but there weren't any obvious demarcations of individual cells wrapped in plastic.

So yeah, it appears that they are being deceptive in labeling it a 12V battery and 8,000 mAh

I think the flat pack is called 'prismatic' configuration, but could be wrong. Most r/c packs are this type.

In any case, there's not much/any cell protection so leave it in the jump start case.

#### lumen aeternum

##### Enlightened
They make power measuring dongles for 120v AC, so you can see what your microwave etc is drawing & how many watts total over a period of time.

We need one for DC voltage loads, to see the battery pack capacity !
Maybe use an electric motor that draws a precise amount of current, with a timer?

#### turbodog

##### Flashlight Enthusiast
They make power measuring dongles for 120v AC, so you can see what your microwave etc is drawing & how many watts total over a period of time.

We need one for DC voltage loads, to see the battery pack capacity !
Maybe use an electric motor that draws a precise amount of current, with a timer?

There are devices like that already. The easy/cheap option is a good r/c charger/discharger. They have settings for li-ion/lipo,Pb,nimh,nicd,etc along with low voltage cutoffs.

Electric motor current will vary depending on voltage. Accuracy would be way off.

#### electromage

##### Enlightened
CPF Supporter
I have a Noco GB40 - I've used it to start many cars that wouldn't start on their own, but results will vary based on the engine size and age, and condition of the starter battery.

Noco has several bigger units than mine, if you have doubts. I would probably get a Boost X 55 now for a little more power and the USB-C charging.

#### orbital

##### Flashlight Enthusiast
With what sounds like a quite dead battery... I think you're gonna have a tough time jump starting it without letting it charge some first. The jump start current would be split between starting and simultaneously trying to charge the battery. Would take some serious power.

That said... I've had very good results from the noco brand of chargers. They also make jump boxes as well.
+

If in the market; the NOCO Boost HD GB70 can be had for \$123 today...
jump, jump, jump