How many 18650 cells can you fit in a 12v 20ah sla form factor

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EHCanadian   100 µW

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How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by EHCanadian » Jun 01 2018 8:20pm

ive been trying to figure out how many 18650 cells you can fit in a 12v 20ah SLA dementions.


Length: 7.13 inches (181mm)
Width: 3 inches (76.2 mm)
Height: 6.57 inches (167mm)

how many ah could I fit in these dementions assuming i am not including a bms and a base voltage of about 10-15v

i currently have 10 12v 20ah SLA batteries on my ebike. Each series connection has its own 12v charge port and charger when i need to balance the sla's. i flip the breaker and can charge that way or if they are within reason of one another i bulk charge with my 3a 120v sla charger.

i have a emmo xtron i basically used as a frame and body kit. did my thing and tore it apart and had a buddy help build a battey box that fits 10 12v 20ah batteries.. it was perfectly fine for the flat city life 90+ km range.. however I have moved up north here in canada and them steep hills and my heavy weight bike can only do about 40km before the batteries r near 100% discharged.. I'm looking to build some drop in replacement 18650 packs to run in series.

Can anyone give their input on how many ah i could cram in parelle and series that does not exceed each battery demention?


Brushless Controller: 120v 80a 36mos
Series wire size: 8 gauge stranded copper.

Voltron   1 MW

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Re: How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by Voltron » Jun 04 2018 11:50am

Man, and people said it was crazy when I had 6 14ah sla's!
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But just to clarify, when you say drop in module, are you replacing all of them at once with lithium, not replacing one lead brick at a time with a same size lithium block as you go along?

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EHCanadian   100 µW

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Re: How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by EHCanadian » Jun 04 2018 3:25pm

Would be all at once as I would build each pack to replace the sla batteries.
I was googling and I guess it would be a 3 series and x parallel pack.

72 Cells in total. 3 in series with 24 in parallel. Thou I can't see that being about the same size or smaller.
72 cells x 10 Packs is 720 cells. Give an extra handful for whoopies.

I may just take a gamble on some of em garbage 18650's from China to get the dimensions and cell count to my answer, But I don't want to waste the Canadian loonies just yet on good cells until I know for sure the minimal mah I would need to meet the 80 amp peak my controller could pull as 18650 models and brands have c limits and unlike SLA.. I can beat 80 amps out of em sla in series and they would just get warm..
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Voltron   1 MW

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Re: How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by Voltron » Jun 04 2018 3:41pm

Have you looked into the big rectangular prismatic cells, say from a Leaf something like that? You're going to be getting into lots and lots of interconnecting and balance port accessibility issues with 18650s... Is switching up to where instead of 10 12v bricks you make some 120v modules to parallel up an option? With the all in series way, any one of the 12v blocks going low will kill the whole series...

P.s. the motor on my bike came from that same type of lead China scooter... So many fun miles after some frame swapping and lithium-ing :)
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Re: How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by Voltron » Jun 04 2018 3:58pm

Another p.s., and somebody might have to check me on this, but does the massive paralleling you're thinking about make it more important to have cell level fusing, as one cell could be self discharging and getting hot in middle of a group with the other 20+ cells dumping juice into it trying to fill it?

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Re: How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by 999zip999 » Jun 04 2018 11:41pm

Drop the sla 12v layout. One big battery is better. Or look into leaf batteries.
You should ask the mods to move this to the battery section you'll get better input

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EHCanadian   100 µW

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Re: How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by EHCanadian » Jun 06 2018 1:35pm

The 12v demention layout is the only option as i would have to tear apart the bike again.

Cell level fuses are a option i am considering.

Since i would be making these packs. I would definitely be adding the option of mainance leads per pack along with direct charging. I am aware it is not going to be cheap but i am looking at doing it right the first time :). Since this is a unique built... rebuilt packs are not a option.
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EHCanadian   100 µW

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Re: How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by EHCanadian » Jul 22 2018 2:34pm

The answer is 81 18650 cells.
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fourbanger   100 W

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Re: How many 18650 cells can you fit in a 12v 20ah sla form factor

Post by fourbanger » Jul 28 2018 2:43am

Yea, I was just going to say, it's 81.

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