This is the best we have found 14 AWG thickness. Easy to solder as its so soft. We keep a large range of batteries, not just for RC models such as LIPO & NIMH's but batteries for bait boats, ride on toy cars, alarms and motorbikes.
eBay
1~50m Flexible Silicone Rubber Cable Copper Wire 2Pins Soft 30 28 26 24 22 20 18 16 14 12 10 8AWG For Car Battery Inverter Motor
Aliexpress UK
Beefy 10 Gauge Silicone Wire by World Champions ACER Racing, Super Flexible 1050 Strands of copper wire. 10 Feet total (5 feet black and 5 feet red wire). Super low electrical resistance for a highly efficient connection.
eBay
Flexible Silicone Wire 0.3 0.5 0.75 1 1.5 2 2.5 4 6mm x 2 3 4 6 Cores Rubber Insulation Tinned Copper High Temperature Cable
Aliexpress UK
【Features】: The wire core consists of multi-strand, high-quality, oxygen-free tinned copper, the insulating layer of the outer skin is made of extra soft silicone rubber, is resistant to high temperatures, can pass large currents, the outer skin is soft and can be easily installed in small model parts.
eBay
1/3/5M Ultra Soft Multi-Core Silicone Rubber Cable 2 3 4 6 Cores 0.3mm²~2.5mm² Flexible Insulated Copper High Temperature Wire
Aliexpress UK
UL3135 Silicone Wire. Gauge:30 28 26 24 22 20 18 16 14 12 10AWG. Conductor:Tinned Copper(OFC). Insulator: Silicone. Internal wiring of household, microwave ovens, printers and electronic devices. Feature: Good softness, wear resistance, high temperature resistance.
eBay
2/5/10M Ultra Soft Multi-Core Silicone Rubber Cable 2 3 4 6 Cores 0.3mm²~2.5mm² Flexible Insulated Copper High Temperature Wire
Aliexpress UK
Wire Gauge: 20AWG (0.5mm²). Flexible Multicore Shielded Cable 0.5mm². For sale: a high-quality silicone-coated multicore cable, ideal for CNC and automation machinery. Type: Machinery 4-core shielded cable.
eBay
1~50m 2Pin Tinned Copper Wire 8 10 12 14 16 18 20 22 24 26 28AWG DIY LED Lamp Connector Flexible Silicone Rubber Cable
Aliexpress UK
red and black silicone wire 16 AWG 25ft red25ft black
eBay
Heat Resistant Flexible Silicone Wire30/28/26/24/22/20/18/16AWG Stranded Cable Electrical Tinned Copper Wire（5 Colors Mix Kit）
Aliexpress UK
Material: Nickel. Size: 500 X 500mm. Size: 600 X 600mm. Warm Reminder: The Picture Is For Reference Only, And The Size, Color, Printing, Etc. Thickness: 1mm. Total Price: 2616 GBP.
eBay
16 18 20 22 24 26 28 30 AWG Flexible Silicone Electrical Wire 6 Colors Stranded Tinned Copper Hookup Insulated Cable
Aliexpress UK
Performance pure silicone wire. High-quality tinned copper inner core, can maintained. Ultra flexible with strong durable thick insulation low resistance, strand wire, high. accessories for high temperature working.
eBay
TOPK L35 Cable Organizer Magnetic Plug Box Silicone Cable Winder Flexible Cable Management Clips for Mouse Earphone
Aliexpress UK