Overview

We will be building a 100Ah LiFePO4 battery using cell modules we purchased from BatteryHookup.com.

Parts

Part	Qty	Picture	URL
3.2V 100ah MODULES	4		https://web.archive.org/web/20210516124542/https://batteryhookup.com/products/new-battery-hookup-lifep04-32650-3-2v-5000mah-cells-1
100A Smart LiFePO4 4S BMS	1		https://batteryhookup.com/products/12v-lifepo4-smart-bms-w-low-temp-cutoff
Bluetooth Module (Optional)	1		https://batteryhookup.com/collections/accessories/products/bluetooth-module-for-battery-hookup-bms https://www.aliexpress.com/item/4000546700379.html?spm=a2g0o.order_list.0.0.21ef1802QOiBrg
50-Cal Black Ammo Box with Tray	1	Dimensions: 15.4 x 10.2 x 7.7 in.	https://www.princessauto.com/en/50-cal-black-ammo-box-with-tray/product/PA0008985962?skuId=8985962
Carkio 8mm (5/16") M8 Stud Premium Remote Battery Power Junction Post Connector Terminal Kit 2pcs	1		https://www.amazon.ca/gp/product/B08J7TGPK5/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&th=1
5/16 Ring Terminals	5
5/16 bolt and lock nut	7
10 AWG Wire (red and black)			Princess Auto
Strap	1		Princess Auto

Modules

These modules were built specifically to handle up to 100a (1c) charge and discharge continuous. Standard lithium ion capacity tests are done at 0.2c which would be 20a continuous. The cells can handle up to 3c but the nickel and wiring was sized to handle 1c loads which is realistically where you want to be.

NOMINAL VOLTAGE	3.2V
CAPACITY	100ah (105ah+ is being reported by customers)
WATT HOURS	320
FULLY CHARGED VOLTAGE	3.65V
FULLY DISCHARGED VOLTAGE	2.5V
MAX CONTINUOUS CHARGE	100A (1C)
MAX CONTINUOUS DISCHARGE	100A (1C)
MAX PULSE DISCHARGE (10 SECONDS)	200A (2C)
MODULE WEIGHT	6.5 lbs
MODULE DIMENSION	7.5" X 5.5" X 3"

BMS

LiFePO4 4S 100a BMS W/ LOW TEMP CUTOFF

Connections

Specifications

Manufacturer	Xiaoxiang
Model	SP04S020A
Configuration	4S 100A
Chemistry	Lifepo4 3.2V
Configuration	Common port with balance
Part Number	16270007

Settings

Overcharge Voltage per Cell	3.65
Over Discharge Voltage per Cell	2.5
Discharge Continuous Amps	100A
10 second Discharge Burst	200A
Charge Continuous Amps	60A
Balancing Current	60mA
Low temp cutoff	32° F (0° C)
High temp cutoff	167° F (75° C)

Bluetooth Module

The Bluetooth module is an optional accessory that may be used to configure and monitor the BMS.

To use, simply plug the 4-pin connector into the BMS. The BMS must be connected to the battery, with the balance lead connected in order for the Bluetooth module to operate.

Note that other Bluetooth modules are not compatible.

For best reception, mount the module high, ideally away from metal. Do not mount it inside of a metal enclosure. The Bluetooth module may be left connected to the BMS for long periods of time. It will go into a deep sleep mode when not in use.

Software (Requires Bluetooth Module)

Build

Battery Case

Measurement	Width/Length/Height
Battery Cell	7.5" X 3" x 5.5"
Battery Cells x 4	7.5" X 12" x 5.5"
Selected Box(Exterior)	7.7" x 15.4" x 10.2"
Selected Box(Interior)	7" x ?

We couldn't find a box with the ideal interior dimension of 7.5" x 12", so we went with this bigger ammo box and placed the cells on their sides.

Cell Top Balancing

In order to ensure we get the max capacity out of our new battery, we need to top balance the cells.

See https://www.youtube.com/watch?v=x5ABvbbics8

Charge the battery in it's 4S configuration and then disassemble.

Connect all cells together in parallel and charge at 3.65v until very little current is flowing into the batteries.

Build Pictures

BMS Configuration

Total Cycle Capacity = your measured capacity.

Capacity Configuration

SoC	Pack Voltage (≈ 4 cells)	Per-Cell Voltage (rested)	What I had	Notes
100 % (just after charge)	14.4 – 14.6 V	3.60 – 3.65 V	3.500	“Surface charge” voltage that will settle to ~13.6 V after resting
100 % (rested)	13.6 V	3.40 V	3.350	Fully charged and rested
90 %	13.4 V	3.35 V	3.330	Nearly topped off
80 %	13.3 V	3.33 V	3.329	Approaching full
70 %	13.2 V	3.30 V	3.325
60 %	13.1 V	3.28 V	3.306
50 %	13.0 V	3.25 V	3.301	Mid-flat plateau
40 %	13.0 V	3.25 V	3.291
30 %	12.9 V	3.23 V	3.280
20 %	12.8 V	3.20 V	3.266	Low end of normal range
10 %	12.0 V	3.00 V	3.220	Very low, nearly empty
0 %	10.0 V	2.50 V	2.500	Absolute minimum – most BMS will cut off here

Balancer Configuration

Spec	Voltage(mV)
Start Voltage	3450
Delta to Balace	15

Suggested Protections

Protection	Per-cell trip → reset	12 V pack (4s) trip → reset	Notes
Over-voltage (OVP)	3.65–3.70 V → 3.40–3.45 V	14.6–14.8 V → 13.6–13.8 V	Trip at top of charge; release after surface charge bleeds.
Under-voltage (UVP)	2.50–2.80 V → 2.90–3.00 V	10.0–11.2 V → 11.6–12.0 V	Give yourself margin; don’t run into UVP in normal use.
Cell balancing start	≈3.45–3.50 V	≈13.8–14.0 V	Passive bleed typically 30–200 mA near top-charge.

Voltage Protection

Spec	Trigger (mv)	Release(mv)	Delay(s)
Cell Over Voltage	3650	3500	2
Cell under Voltage	2500	2800	2
Battery Over Voltage	14600	14000	2
Battery Under Voltage	10000	11200	2

Current Protection

Spec	Trigger(mA)	Release (s)	Delay(s)
Charge Over Current	100000	32	10
Discharge Over Current	100000	32	10

Temp Protection

Spec	Trigger(*C)	Release (*C)	Delay(s)
Charge Over Temp	65	55	2
Charge Under Temp	-1	5	2
Discharge Over Temp	75	70	2
Discharge Under Temp	-10	0	2

Capacity Tests

Capacity Test - 2022 (New)

Battery Tests @ 10A Load

Battery	Capacity Ah
1	112 Ah
2	95 Ah
2 (After Top Balancing)	118 Ah

Capacity Test - Oct 2025

Battery 1 Cell Capacity

This test was done after top balancing the cells.

Cell	1	2	3	4	Avg
Capacity	108.1	107.6	103.9	107.5	106.8

Battery 2 Cell Capacity

This test was done after top balancing the cells.

Cell	1	2	3	4	Avg
Capacity	107.4	105.9	106.0	108.2	106.9

Battery Re-Config

Battery 1

Cell	1	2	3	4	Avg
Capacity	108.1	107.6	108.2	107.5	107.9

Battery 2

Cell	1	2	3	4	Avg
Capacity	107.4	105.9	106.0	103.9	105.8

Battery	Capacity Ah
1	110.4 Ah
2	106.7 Ah

Cost Breakdown

I ordered enough to build 3 batteries in order to save on shipping.

Item	Cost	Currency	Exchange Rate	CA$
4 x 3.2V 100ah MODULES $240.00 US - 5% Discount	$228.00	US	0.750410380676933	$303.83
Smart BMS $74.99.00 US - 5% Discount	$71.24	US	0.750410380676933	$94.93
Shipping ($68.35/3)	$22.78	US	0.750410380676933	$30.35
Duty ($145.41/3)	$48.47	CA	-	$48.47
My USAddress ($12.00/3)	$4.00	US	0.750410380676933	$5.33
Bluetooth Module	$10.16	CA	-	$10.16
Power Junction Post ($48.96/3)	$16.32	CA	-	$16.32
				$509.39

Other Costs

Item	Cost	Currency	Exchange	CA$
Ammo Box ($16.99 + HST)	$19.19	CA	-	$19.19
5x 5/16" Ring Terminal
10 AWG Red Wire
10 AWG Black Wire
Solder	-
Strap	$3.00
Heat Shrink Tubing
5/16 Nuts and Bolts
Zip Ties
Duct Tape
Total

Appendix

BMS Protocol

Command

Response

Baud Rate: 9600 bps

Sample - Read Info

Command

StartBit	Read/Write	Command	Length	Data	Checksum	StopBit
DD	A5	03	00	-	FF FD	77

Checksum Calculation = (Command + Length + Data) XOR 0xFFFF + 1

= (0x03 + 0x00) XOR 0xFFFF + 1

= 0xFFFD

Response

StartBit	Command	Status	Length	Data	Checksum	StopBit
DD	03	00	1B	17 00 00 00 02 D0 03 E8 00 00 20 78 00 00 00 00 00 00 10 48 03 0F 02 0B 76 0B 82	FB FF	77

Checksum Calculation = (Status + Length + Data) XOR 0xFFFF + 1

= 0x00 + 0x1B + data[] XOR 0xFFFF +1

= 0x0401 XOR 0xFFF + 1

= 0xFBFE + 1

= 0xFBFF

References

Reference	URL
Smart BMS	https://batteryhookup.com/products/12v-lifepo4-smart-bms-w-low-temp-cutoff
3.2V 100ah MODULES	https://web.archive.org/web/20210516124542/https://batteryhookup.com/products/new-battery-hookup-lifep04-32650-3-2v-5000mah-cells-1
BMS Manual	bms_series.pdf
Xiaoxiang BMS Manual	https://github.com/smagicld/xiaoxiangBMS
Software	https://www.lithiumbatterypcb.com/smart-bms-software-download/
OverkillSolar BMS Files	https://github.com/FurTrader/OverkillSolarBMS
Arduino Library	https://github.com/FurTrader/OverkillSolarBMS/tree/master/Arduino
Communication Protocol	JBD Protocol English version.pdf
Communication Protocol	Protocol English Version.pdf
Build Video $420 100AH LiFePO4 Build - BatteryHookup.com Modules - Super Easy Assembly! COMPLETE DIY GUIDE!	https://www.youtube.com/watch?v=uN1h0XIpfTg&t=1401s
DIY 100AH LIFEPO4 BATTERY PARTS LIST	https://jasonoid.com/diy100ahlifepo4/
How to Top Balance LiFePO4 Battery Cells Quickly (and when you need to do it)	https://www.youtube.com/watch?v=x5ABvbbics8

Space shortcuts

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Overview

Parts

Modules

BMS

Connections

Specifications

Settings

Bluetooth Module

Software (Requires Bluetooth Module)

XiaoXang BMS

Big Battery

XiaoXiang Electric

Build

Battery Case

Cell Top Balancing

Build Pictures

BMS Configuration

Capacity Tests

Capacity Test - 2022 (New)

Capacity Test - Oct 2025

Cost Breakdown

Appendix

BMS Protocol

References

Space shortcuts

Page tree

LiFePO4 100Ah Battery Build

Overview

Parts

Modules

BMS

Connections

Specifications

Settings

Bluetooth Module

Software (Requires Bluetooth Module)

XiaoXang BMS

Big Battery

XiaoXiang Electric

Build

Battery Case

Cell Top Balancing

Build Pictures

BMS Configuration

Capacity Tests

Capacity Test - 2022 (New)

Capacity Test - Oct 2025

Cost Breakdown

Appendix

BMS Protocol

References