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) |
11.6840 0.4600 |
107.2193 0.1662 |
0.1608 0.04901 |
195 | 230 | 260 |
| 3/0 (000) |
10.4049 0.4096 |
85.0288 0.1318 |
0.2028 0.06180 |
165 | 200 | 225 |
| 2/0 (00) |
9.2658 0.3648 |
67.4309 0.1045 |
0.2557 0.07793 |
145 | 175 | 195 |
| AWG 0 (1/0) | 8.2515 0.3249 |
53.4751 0.0829 |
0.3224 0.09827 |
125 | 150 | 170 |
| 1 | 7.3481 0.2893 |
42.4077 0.0657 |
0.4066 0.1239 |
110 | 130 | 145 |
| 2 | 6.5437 0.2576 |
33.6308 0.0521 |
0.5127 0.1563 |
95 | 115 | 130 |
| 3 | 5.8273 0.2294 |
26.6705 0.0413 |
0.6465 0.1970 |
85 | 100 | 115 |
| AWG 4 | 5.1894 0.2043 |
21.1506 0.0328 |
0.8152 0.2485 |
70 | 85 | 95 |
| 5 | 4.6213 0.1819 |
16.7732 0.0260 |
1.028 0.3133 |
- | - | - |
| AWG 6 | 4.1154 0.1620 |
13.3018 0.0206 |
1.296 0.3951 |
55 | 65 | 75 |
| 7 | 3.6649 0.1443 |
10.5488 0.0164 |
1.634 0.4982 |
- | - | - |
| AWG 8 | 3.2636 0.1285 |
8.3656 0.0130 |
2.061 0.6282 |
40 | 50 | 55 |
| 9 | 2.9064 0.1144 |
6.6342 0.0103 |
2.599 0.7921 |
- | - | - |
| AWG 10 | 2.5882 0.1019 |
5.2612 0.0082 |
3.277 0.9989 |
30 | 35 | 40 |
| 11 | 2.3048 0.0907 |
4.1723 0.0065 |
4.132 1.260 |
- | - | - |
| AWG 12 | 2.0525 0.0808 |
3.3088 0.0051 |
5.211 1.588 |
20 | 25 | 30 |
| 13 | 1.8278 0.0720 |
2.6240 0.0041 |
6.571 2.003 |
- | - | - |
| AWG 14 | 1.6277 0.0641 |
2.0809 0.0032 |
8.286 2.525 |
15 | 20 | 25 |
| 15 | 1.4495 0.0571 |
1.6502 0.0026 |
10.45 3.184 |
- | - | - |
| 16 | 1.2908 0.0508 |
1.3087 0.0020 |
13.17 4.016 |
- | - | 18 |
| 17 | 1.1495 0.0453 |
1.0378 0.0016 |
16.61 5.064 |
- | - | - |
| AWG 18 | 1.0237 0.0403 |
0.8230 0.0013 |
20.95 6.385 |
10 | 14 | 16 |
| 19 | 0.9116 0.0359 |
0.6527 0.0010 |
26.42 8.051 |
- | - | - |
| 20 | 0.8118 0.0320 |
0.5176 0.0008 |
33.31 10.15 |
5 | 11 | - |
| 21 | 0.7229 0.0285 |
0.4105 0.0006 |
42.00 12.80 |
- | - | - |
| 22 | 0.6438 0.0253 |
0.3255 0.0005 |
52.96 16.14 |
3 | 7 | - |
| 23 | 0.5733 0.0226 |
0.2582 0.0004 |
66.79 20.36 |
- | - | - |
| 24 | 0.5106 0.0201 |
0.2047 0.0003 |
84.22 25.67 |
2.1 | 3.5 | - |
| 25 | 0.4547 0.0179 |
0.1624 0.0003 |
106.2 32.37 |
- | - | - |
| 26 | 0.4049 0.0159 |
0.1288 0.0002 |
133.9 40.81 |
1.3 | 2.2 | - |
| 27 | 0.3606 0.0142 |
0.1021 0.0002 |
168.9 51.47 |
- | - | - |
| 28 | 0.3211 0.0126 |
0.0810 0.0001 |
212.9 64.90 |
0.83 | 1.4 | - |
| 29 | 0.2859 0.0113 |
0.0642 0.0001 |
268.5 81.84 |
- | - | - |
| 30 | 0.2546 0.0100 |
0.0509 0.0001 |
338.6 103.2 |
0.52 | 0.86 | - |
| 31 | 0.2268 0.0089 |
0.0404 0.0001 |
426.9 130.1 |
- | - | - |
| 32 | 0.2019 0.0080 |
0.0320 0.0000 |
538.3 164.1 |
0.32 | 0.53 | - |
| 33 | 0.1798 0.0071 |
0.0254 0.0000 |
678.8 206.9 |
- | - | - |
| 34 | 0.1601 0.0063 |
0.0201 0.0000 |
856.0 260.9 |
0.18 | 0.3 | - |
| 35 | 0.1426 0.0056 |
0.0160 0.0000 |
1079 329.0 |
- | - | - |
| 36 | 0.1270 0.0050 |
0.0127 0.0000 |
1361 414.8 |
- | - | - |
| 37 | 0.1131 0.0045 |
0.0100 0.0000 |
1716 523.1 |
- | - | - |
| 38 | 0.1007 0.0040 |
0.0080 0.0000 |
2164 659.6 |
- | - | - |
| 39 | 0.0897 0.0035 |
0.0063 0.0000 |
2729 831.8 |
- | - | - |
| 40 | 0.0799 0.0031 |
0.0050 0.0000 |
3441 1049 |
- | - | - |
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!
Now, let's return to our 6 gauge wire:
- 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.
