How to create a battery pack with 18650 batteries similar or better to this "12v/7ah/20h" battery?

[Kashgar]

Hello everyone! been thinking to do this project for a while now and very happy to find this community literally today from Will Prowse's youtube channel. also thanks for looking.

I got about 20 plus of those LG HG2 18650 Flat Top batteries off of eBay, all-new batteries. that said, I wanted to build a battery pack that has similar power and capacity with my kids' 12v car battery that reads 12v/7ah/20h. after pulling out the little car's battery which I'll be attaching the pictures of the battery along with its charger, I'm kinda lost and don't know where to begin. I hope to get help over here about how to do it exactly. like how to put up those 18650 batteries along with the proper type of BMS and finally with a proper charger.

Thanks a lot

 

[John Frum]

Welcome to the forum.

Assuming you mean one of the vent with fire chemistries.
the nominal voltage for those is 3.7 volts per cell.
3 cells in series is 11.1 volts.
The maximum charging voltage is 12.6 volts.
If each cell was rated at 7ah(amp hours)
Then 3 is series is 12v/7ah
The 20h part doesn't really apply to lithium chemistries.
If your cells were rated at 3.5 amp hours then you need to make 3 sets of 2 cells in parallel.
Then connect the sets in series to make a 7 amp hour@12 volt battery.

Its very important to add a battery managment system(bms) to these kinds of batteries as they can vent with fire.

Hope that helps.
I expect will have follow up questions.

 

[Kashgar]

Thank you so much for your response! i really appreciate it!
the 18650 batteries I have: just copied off from the eBay seller's post.

LG Brown HG2 INR18650 3000mah 18650 Battery
The authentic LG Brown HG2 INR18650 3000mah Battery caters to every wish for high-drain and high-capacity. With this latest battery from LG 20A constant current and killer 35A pulse will keep you going all day.
High Drain- 20A constant current, 35A pulse current load.
Model: LG 18650 HG2
Nominal Capacity: 3000mAh
Nominal Voltage: 3.6V
Full charge Voltage: 4.2V
Operating Temperature (cell surface): Charge 0 ~ 50℃, Discharge -20 ~ 75℃
Diameter : 18.3 + 0.2/-0.3 mm ( Max. 18.5 mm )
Height : 65.0 ± 0.2 mm ( Max. 65.2 mm )
Weight Max. 48.0 g
Positive terminal: Flat top

Can get more if needed for the build.
I'm just tired of the quality of that Sealed Lead Acid battery and thus I wanted something better.

 

[Kashgar]

Welcome to the forum.

Assuming you mean one of the vent with fire chemistries.
the nominal voltage for those is 3.7 volts per cell.
3 cells in series is 11.1 volts.
The maximum charging voltage is 12.6 volts.
If each cell was rated at 7ah(amp hours)
Then 3 is series is 12v/7ah
The 20h part doesn't really apply to lithium chemistries.
If your cells were rated at 3.5 amp hours then you need to make 3 sets of 2 cells in parallel.
Then connect the sets in series to make a 7 amp hour@12 volt battery.

Its very important to add a battery managment system(bms) to these kinds of batteries as they can vent with fire.

Hope that helps.
I expect will have follow up questions.

Thank you so much for your response! i really appreciate it!
the 18650 batteries I have: just copied off from the eBay seller's post.

LG Brown HG2 INR18650 3000mah 18650 Battery
The authentic LG Brown HG2 INR18650 3000mah Battery caters to every wish for high-drain and high-capacity. With this latest battery from LG 20A constant current and killer 35A pulse will keep you going all day.
High Drain- 20A constant current, 35A pulse current load.
Model: LG 18650 HG2
Nominal Capacity: 3000mAh
Nominal Voltage: 3.6V
Full charge Voltage: 4.2V
Operating Temperature (cell surface): Charge 0 ~ 50℃, Discharge -20 ~ 75℃
Diameter : 18.3 + 0.2/-0.3 mm ( Max. 18.5 mm )
Height : 65.0 ± 0.2 mm ( Max. 65.2 mm )
Weight Max. 48.0 g
Positive terminal: Flat top

Can get more if needed for the build.
I'm just tired of the quality of that Sealed Lead Acid battery and thus I wanted something better.

 

[John Frum]

Nominal Capacity: 3000mAh
Nominal Voltage: 3.6V
Full charge Voltage: 4.2V
Operating Temperature (cell surface): Charge 0 ~ 50℃, Discharge -20 ~ 75℃

Ok that confirms the cells are the "vent with fire" variety.
Have you considered lifepo4?
Lifepo4 is much safer and its voltage range is more appropriate to replace a 12 volt lead acid battery.
2 of the above cells in parallel is 6 amp hours.
3 in parallel is 9 amp hours.

 

[Kashgar]

Welcome to the forum.

Assuming you mean one of the vent with fire chemistries.
the nominal voltage for those is 3.7 volts per cell.
3 cells in series is 11.1 volts.
The maximum charging voltage is 12.6 volts.
If each cell was rated at 7ah(amp hours)
Then 3 is series is 12v/7ah
The 20h part doesn't really apply to lithium chemistries.
If your cells were rated at 3.5 amp hours then you need to make 3 sets of 2 cells in parallel.
Then connect the sets in series to make a 7 amp hour@12 volt battery.

Its very important to add a battery managment system(bms) to these kinds of batteries as they can vent with fire.

Hope that helps.
I expect will have follow up questions.

Also, about the voltage, based on YouTubers, saw them turning those little cars faster by 18v batteries. I'm assuming putting 4 of these 18650 in series may give a little better kick as compared to the original 12v. for the amps, for longer use, I'd like to increase a bit if it's viable.
if so, what BMS i should get? if i can get a link for those, it would be perfect. Thank you again.

 

[Kashgar]

Ok that confirms the cells are the "vent with fire" variety.
Have you considered lifepo4?
Lifepo4 is much safer and its voltage range is more appropriate to replace a 12 volt lead acid battery.
2 of the above cells in parallel is 6 amp hours.
3 in parallel is 9 amp hours.

I like the 9 amp idea!
the lifepo4, frankly, I don't know that I'm new to this whole battery build stuff. Recently, began, following Will's channel, somehow, and now so interested in those builds...

 

[Supervstech]

LFP is a much better match for the vehicle, but you can use the cells you have.
Get a 4s BMS, AND a 16V lithium charger.
2p4s will be a long life fast little car!

 

[John Frum]

LFP is a much better match for the vehicle, but you can use the cells you have.
Get a 4s BMS, AND a 16V lithium charger.
2p4s will be a long life fast little car!

I think 3s is a better fit.

 

[Kashgar]

I think 3s is a better fit.

Okay. so it's 2p3s then?

 

[Kashgar]

Ok that confirms the cells are the "vent with fire" variety.
Have you considered lifepo4?
Lifepo4 is much safer and its voltage range is more appropriate to replace a 12 volt lead acid battery.
2 of the above cells in parallel is 6 amp hours.
3 in parallel is 9 amp hours.

I did check the Lifepo4 battery real quick. like the Battleborn and such. are there smaller size models?

 

[Kashgar]

I think 3s is a better fit.

Is this okay? can I use it with the existing charger?

 

[John Frum]

Is this okay? can I use it with the existing charger?

Max charging current is 5 amps.
2.5 amps is likely optimal.

 

[John Frum]

The expertpower battery can be safely discharged to 80%.
As opposed to a lead acid battery that can only be discharged to 50%.

 

[Supervstech]

Is this okay? can I use it with the existing charger?

No
Not in 3s, MAX 12.6V, means the SLA 14V Charger will burst the batteries in flames...

If you use LFP cells in 4s, they will be ok on the stock charger.

 

[Supervstech]

I think 3s is a better fit.

Really? 3.7V nominal 3s gives 11.1 v in the meat range of charge... kinda low for a tyke car... 14.8 in the meat, and safe to charge up to 16.8V... also, the higher voltage will put a little spunk in the car like he is asking.

 

[John Frum]

Really? 3.7V nominal 3s gives 11.1 v in the meat range of charge... kinda low for a tyke car... 14.8 in the meat, and safe to charge up to 16.8V... also, the higher voltage will put a little spunk in the car like he is asking.

I missed the application, you are correct.

 

[Supervstech]

Is this okay? can I use it with the existing charger?

No idea why I didn’t see the picture the first time... but the pictured battery is a drop in LiFePO4 battery, and will work ok with the stock charger... not PERFECT for the battery, but safe.

 

[Kashgar]

No idea why I didn’t see the picture the first time... but the pictured battery is a drop in LiFePO4 battery, and will work ok with the stock charger... not PERFECT for the battery, but safe.

thank you so much!

 

[Kashgar]

The expertpower battery can be safely discharged to 80%.
As opposed to a lead acid battery that can only be discharged to 50%.

thank you so much for everything!