# What Gauge Wire Is Needed To Connect 12V Batteries?

When connecting batteries in series and parallel, it is important to know the maximum current that will go through the wires and the length of the wires.

12V lead-acid and lithium batteries are able to provide very strong currents, but if too thin wires are used, energy losses may be unacceptable. Also, overheating of the wires and even fires are easily possible.

Published: November 14, 2022.

## Wire Ampacity and Wire Gauge Chart

Wire Ampacity is the ability of the wire to carry current without "too high" energy losses - we will talk about this "too high" later.

Generally, the thicker the wire, the lower the energy losses. However, thicker wires are more difficult to work with, even stranded ones.

The following comparison chart lists wire thicknesses and their default Ampacities for three different maximum wire surface temperatures:

 AWG# Diameter(mm/inches) Area(mm2/in2) Resistance (Copper)(mΩ/m;mΩ/ft) Ampacity (A) @60°C/140°F @75°C/167°F @90°C/194°F 4/0(0000) 11.68400.4600 107.21930.1662 0.16080.04901 195 230 260 3/0(000) 10.40490.4096 85.02880.1318 0.20280.06180 165 200 225 2/0(00) 9.26580.3648 67.43090.1045 0.25570.07793 145 175 195 AWG 0 (1/0) 8.25150.3249 53.47510.0829 0.32240.09827 125 150 170 1 7.34810.2893 42.40770.0657 0.40660.1239 110 130 145 2 6.54370.2576 33.63080.0521 0.51270.1563 95 115 130 3 5.82730.2294 26.67050.0413 0.64650.1970 85 100 115 AWG 4 5.18940.2043 21.15060.0328 0.81520.2485 70 85 95 5 4.62130.1819 16.77320.0260 1.0280.3133 - - - AWG 6 4.11540.1620 13.30180.0206 1.2960.3951 55 65 75 7 3.66490.1443 10.54880.0164 1.6340.4982 - - - AWG 8 3.26360.1285 8.36560.0130 2.0610.6282 40 50 55 9 2.90640.1144 6.63420.0103 2.5990.7921 - - - AWG 10 2.58820.1019 5.26120.0082 3.2770.9989 30 35 40 11 2.30480.0907 4.17230.0065 4.1321.260 - - - AWG 12 2.05250.0808 3.30880.0051 5.2111.588 20 25 30 13 1.82780.0720 2.62400.0041 6.5712.003 - - - AWG 14 1.62770.0641 2.08090.0032 8.2862.525 15 20 25 15 1.44950.0571 1.65020.0026 10.453.184 - - - 16 1.29080.0508 1.30870.0020 13.174.016 - - 18 17 1.14950.0453 1.03780.0016 16.615.064 - - - AWG 18 1.02370.0403 0.82300.0013 20.956.385 10 14 16 19 0.91160.0359 0.65270.0010 26.428.051 - - - 20 0.81180.0320 0.51760.0008 33.3110.15 5 11 - 21 0.72290.0285 0.41050.0006 42.0012.80 - - - 22 0.64380.0253 0.32550.0005 52.9616.14 3 7 - 23 0.57330.0226 0.25820.0004 66.7920.36 - - - 24 0.51060.0201 0.20470.0003 84.2225.67 2.1 3.5 - 25 0.45470.0179 0.16240.0003 106.232.37 - - - 26 0.40490.0159 0.12880.0002 133.940.81 1.3 2.2 - 27 0.36060.0142 0.10210.0002 168.951.47 - - - 28 0.32110.0126 0.08100.0001 212.964.90 0.83 1.4 - 29 0.28590.0113 0.06420.0001 268.581.84 - - - 30 0.25460.0100 0.05090.0001 338.6103.2 0.52 0.86 - 31 0.22680.0089 0.04040.0001 426.9130.1 - - - 32 0.20190.0080 0.03200.0000 538.3164.1 0.32 0.53 - 33 0.17980.0071 0.02540.0000 678.8206.9 - - - 34 0.16010.0063 0.02010.0000 856.0260.9 0.18 0.3 - 35 0.14260.0056 0.01600.0000 1079329.0 - - - 36 0.12700.0050 0.01270.0000 1361414.8 - - - 37 0.11310.0045 0.01000.0000 1716523.1 - - - 38 0.10070.0040 0.00800.0000 2164659.6 - - - 39 0.08970.0035 0.00630.0000 2729831.8 - - - 40 0.07990.0031 0.00500.0000 34411049 - - -

Note: Ampacities are given for enclosed wires @86°F (@30°C) ambient temperatures.

However, these values can't be directly used when trying to find the wire thickness/gauge for the 12V battery.

If the wires are going to be short, less than 50ft (~15m), then only the "80% Rule" is being used.

For example:

6 gauge wire features a default Ampacity of 55 Amps for a maximum wire surface temperature of 60°C/140°F.

However, for safety reasons, the 80% Rule is applied:

IMax = 55 Amps * 0.8 = 44 Amps

So, we can say that for shorter 6 gauge wires (less than 50ft), the maximum allowed continuous current is 44 Amps - and this result only takes into account the maximum allowed wire surface temperature, which is generally enough for thicker wires, but it is also nice to know exact energy losses.

Note: when the wires are longer than 50ft, the Ampacity is decreased by 10% for every 50ft. However, if You need such long wires for 12V batteries, are You sure that You can't move your battery (or battery pack) closer to the load being powered by your battery/battery pack? You are going to end up with rather thick wires...

The following chart lists some of the wire sizes for the most common currents the 12V batteries are required to provide, and energy losses which are calculated per 1m of wire:

 AWG Resistance(mΩ/m) Ampacity (A) @60°C/140°F Energy Losses/Energy Transferred(Watts @80% Amps per 1m of wire) Default Ampacity 80% Rule Applied 4/0 (0000) 0.1608 195 156 3.91W of 1872W: 0.208% 3/0 (000) 0.2028 165 132 3.53W of 1584W: 0.223% 2/0 (00) 0.2557 145 116 3.44W of 1392W: 0.247% 1/0 (0) 0.3224 125 100 3.22W of 1200W: 0.268% 1 0.4066 110 88 3.15W of 1056W: 0.298% 2 0.5127 95 76 2.96W of 912W: 0.324% 3 0.6465 85 68 2.99W of 816W: 0.366% 4 0.8152 70 56 2.56W of 672W: 0.381% 6 1.296 55 44 2.51W of 528W: 0.475% 8 2.061 40 32 2.11W of 384W: 0.549% 10 3.277 30 24 1.88W of 288W: 0.653% 12 5.211 20 16 1.33W of 192W: 0.693% 14 8.286 15 12 1.19W of 144W: 0.826% 18 20.95 10 8 1.34W of 96W: 1.396%

Note: we have really tried to verify every single bit of information in this chart (and complete site, of course), but there are no warranties of any kind! Use your common judgment and if unsure, contact a local certified professional electrician or company!

• Default Ampacity: 55 Amps
• 80% Rule Applied: 55 Amps * 0.8 = 44 Amps
• Resistance of 6 gauge solid copper wire: 1.296 mΩ per 1m of wire
• Energy losses in 1m of 6 gauge solid copper wire (I=max): PLoss/1m = R * I2 = 0.001296 * 442 = 2.509056 = ~2.51W
• Total Battery Power: Pbat = I * U = 44A * 12V = 528W
• Energy losses in 1m of 6 gauge solid copper wire (I=max): ~2.51W/528W = 0.0047537878 = ~ 0.00475 = ~0.475%

So, if You have a 12V battery and 2m cable consisting of 2x 2m 6 gauge wire powering a DC load (a trolling motor, for example) that draws 44 Amps, then:

• Battery Power: 12V * 44 A = 528W
• Energy/Power Losses: 0.001296 Ω/m * (44A)2 * 4m = 10.036W → 10.036W/528W = 0.019008 = ~1.9%

In this example, the battery provides 528W, while the load receives ~518W of power, and 10 Watts are lost in wires in the form of heat.

So, for short and thick wires, default Ampacity with the applied 80% Rule provides us with wires and cables that have relatively low energy losses (and surface temperature well below 60°C/140°F).

But, if we want to calculate exact energy losses in the cables, and if we want to keep them below 3%, we have to calculate exact power/energy losses and find out which gauge wire is the best in terms of thickness, but also weight, and price.

Again, if unsure, contact a local certified electrician or company! Although 12V voltage is considered safe to work with, 12V batteries can nonetheless provide huge currents that can cause injuries (or worse), fires, and similar.