Copper is 0.005" (0.127 mm) thick.
Battery build cost breakdown:
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3 x LG 36V 4.4AH Hooverboard battery packs (for 60 salvaged new old stock LG MF1 cells) : 3 x 35.99 USD = 107.97 USD
Source: "NEW LG 36V 4.4AH BATTERY PACK 18650 EBIKE VAPE POWERWALL BATTERIES 20 CELLS BMS"

Seller Alarmhookup on eBay : https://www.ebay.com/usr/alarmhookup?_trksid=p2047675.l2559
You'd have to watch for when he will have some more. Last time I checked when they were available, price had gone up to 44.99 USD per 20 cell pack... These have LG MF1 cells (each 2150 mAh, 10A capable, 3.65V nominal .... manufacture date code from Sept and Oct 2016).
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1 x 108pcs 18650 rewrap sleeves + carboard protective rings (only used 60) : 1 x 7.99 USD = 7.99 USD
Source: 108 pcs Pre-Cut 18650 Insulator and LIME GREEN PVC Heat Shrink Wrap Vape ebike https://www.ebay.com/itm/108-pcs-Pre-Cut-18650-Insulator-and-LIME-GREEN-PVC-Heat-Shrink-Wrap-Vape-ebike/132514747349?hash=item1eda7e93d5:g:50IAAOSwSrVaj4F7
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3 x 2pcs 10 cells Honeycomb minimal bulkness 18650 holders (only used 5 outta 6 holders): 3 x 1.99 USD = 5.97 USD
Source: 2X 10 plastic holder 18650 battery holder Cylindrical cell bracket plastic case https://www.ebay.com/itm/2pcs-10x-Cell-Plastic-18650-Battery-Spacer-Holder-Cylindrical-Cell-Bracket-Case/302687058301?hash=item46798df97d:g

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- K&S Precision Metal 0.005" (0.127mm) thick roll of 110 grade (aka C11000) min 99.9% pure Copper sheet 12 feet by 12 inch.
16.99$ from K&S Precision Metal (Item stock number : #6020) : 16.99 USD
Source: https://endless-sphere.com/forums/viewtopic.php?f=14&t=89076&p=1390372&hilit=6020+copper#p1390372
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1 x 14S 45A Balancing BMS: 1 x 15.96 USD = 15.96 USD
Source: 14S 51.8V 45A BMS PCB PCM for ebike electric bicycle 18650 Li-ion LIPO battery https://www.ebay.com/itm/14S-51-8V-45A-BMS-PCB-PCM-for-ebike-electric-bicycle-18650-Li-ion-LIPO-battery/112636580964?hash=item1a39a9d464:g:ywgAAOSwWfdbD7rq
1 x 1 Male and 1 female Amass XT60 connector (Bought 5 pair for 11.58 USD, so one pair = 2.32 USD
Source: 5x Amass XT60H XT60+ Male/Female Connector Plug for Battery ESC & Charge Lead https://www.ebay.com/itm/5x-Amass-XT60H-XT60-Male-Female-Connector-Plug-for-Battery-ESC-Charge-Lead/223129895688?hash=item33f3940308:g:AQsAAOSwo4pYg5BY
1 x 12 AWG 10 feet (5 ft red + 5 ft black) silicon wire = 5.50 USD (price have gone up since last year though...)
Source: 12 AWG 10 Feet Gauge Silicone Wire Flexible Stranded Cables for RC Black+Red ED https://www.ebay.com/itm/12-AWG-10-Feet-Gauge-Silicone-Wire-Flexible-Stranded-Cables-for-RC-Black-Red-ED/112138929314?epid=1373853081&hash=item1a1c0044a2
1 x Battery gauge indicator (3S up to 15S Li-Ion) = 3.68 USD
Source : 12V 24V 36V 48V LCD Battery Capacity Tester Indicator car Lead-acid Lithium Cell https://www.ebay.com/itm/12V-24V-36V-48V-LCD-Battery-Capacity-Tester-Indicator-car-Lead-acid-Lithium-Cell/222293145050?hash=item33c1b435da:g:-woAAOSwXeJYD11M
1 x 2 meter (used only 1 meter or so) 14 mm Protective Wire Braided sleeve = 3.59 USD
Source: 3mm~100mm Black Tight Braided PET Expandable Sleeving Cable Wire Sheath lot https://www.ebay.com/itm/3mm-100mm-Black-Tight-Braided-PET-Expandable-Sleeving-Cable-Wire-Sheath-lot/192053564552?var=491892214796&hash=item2cb748d488:m:m-nHfjUcipq22tNrOsRQhLA
1 x 1 roll of 33meter x 50 mm wide Foxnovo High Temperature Heat Resistant Kapton Tape Polyimide Film Adhesive Tape (50mm*33m) = 10.99 USD
Source: https://www.amazon.com/dp/B00N1QZY4M/ref=twister_B00N2QJ9PG?_encoding=UTF8&th=1
Total cost of battery :
181.97 USD. Now I just need to find padding, affix the batt meter and shrinkwrap.
This battery is made of 56 LG MF1 cells. My pack specs are:
14S 18650 LiNiMnCoO2 - 8.6Ah 51.1V nominal (min 38.5V, max 58.8V), max 40A load, 439.5 Wh. Std chrg rate 2.15A. Max chrg rate 8.6A
58.8V 2A Charger : (had to solder some XT60 to charger leads):
33.89 USD - Generic 58.8V 2A Electric Bike Lithium Battery Charger for 48V Lithium Battery Pack https://www.amazon.com/Generic-Electric-Lithium-Battery-Charger/dp/B071FBGG7S/ref=sr_1_1?ie=UTF8&qid=1538240910&sr=8-1&keywords=Generic+58.8V+2A+Electric+Bike+Lithium+Battery+Charger+for+48V+Lithium+Battery+Pack
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