I am making a big project soon, a spider robot, and I will have a total of 4 batteries. 2 batteries will be wired in parallel and 2 in series, and then those 2 packs of 2 each in parallel.I don't want to have to disconnect them every time I use it, but I will if it drains. So my question is straight forward, will leaving the spider off, but the batteries still connected in the circuit, drain the batteries? I can't find it on google. I noticed the batteries get hot when I tested both volts and amps with my multi-meter. So I figured, it is draining. Is it? I hope this isn't a stupid question.

  • \$\begingroup\$ parallel drain occurs from mismatched voltages when not in use if the resting voltage differs if separated, while series excess drain if the capacity is lower and/or ESR is higher. Both demand balanced cells <2% unless protected but shorter lifespan of series weakest cell influences total capacity when used and in parallel can affect all cells \$\endgroup\$ Feb 22, 2017 at 3:14
  • \$\begingroup\$ Well, the batteries I am using is new and rechargeable. I tested the voltage of them and it is about the same. I got the 3.7 volts at 3000 mAh ones. I could not test the amps for some odd reason. My multimeter was at at 10 Amps, did not read anything. It is a lot more than 3000mAh. Anyways, they should be matched. So if they are matched with less than 2%, it is good then? \$\endgroup\$
    – Sean.D
    Feb 22, 2017 at 3:19
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    \$\begingroup\$ Amazon is buyer's risk, no guarantee. You get to hope to receive what they advertise which is poorly defined. If you can't measure on the 10A socket & scale either you are using the meter wrong or the fuse is blown. "My multimeter was at at 10 Amps, did not read anything. " \$\endgroup\$ Feb 22, 2017 at 3:40
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    \$\begingroup\$ DO NOT EVER attempt to measure the available current from a battery or other power source by connecting a meter set to read Amps directly across the battery - the meter will short-circuit the battery, and excessive current will flow. Any "measurement" you get this way is meaningless. \$\endgroup\$ Feb 22, 2017 at 3:40
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    \$\begingroup\$ Draw a diagram of how the batteries are connected. I can't quite figure it out. You say two in series and two in parallel, and then connect them together. It doesn't make any sense. Draw a diagram showing all the batteries. \$\endgroup\$
    – mkeith
    Feb 22, 2017 at 4:11

1 Answer 1


You cannot just wire batteries together at random and expect things not to blow up.

You created two packs. One has double the voltage of a single battery, one has double the amperage of a single battery.

Then you short-circuit those packs which differ by the voltage of a single battery. The double-voltage pack will now violently drain into the double-amperage pack. The double-voltage pack will likely die of over-current while the double-amperage pack will die of over-voltage.

Depending on the kind of batteries, they might melt wires in the process or catch fire.

So now you have your violently reorganising doomsday battery device. And you put an amperemeter across it. An ideal amperemeter measures the current running through it without causing an external voltage, so its internal resistance is as close to zero as possible, like a piece of thick wire.

So you now use your amperemeter in order to shortcircuit the remnants of your suicide battery pack and drain all the current it can spare in light of your previous abuse.

Which apparently is still more than the fuse of the amperemeter would have tolerated.

Exploding batteries can cause a lot of damage, but they tend to be comparatively affordable unless we are talking really large ones. I would seriously recommend that you have someone look over your wiring before and while you start hooking it up with any power source, or your large project might become a pretty expensive project due to destroyed parts.

  • \$\begingroup\$ Well, the only problem with my project is power. I need 6A and 7.4 volts of power. I have a thread on the arduino stack exchange explaining the circuit of all the parts and what power I need. Here that forum: arduino.stackexchange.com/questions/34768/… So since the only problem is power, could I do what mkeith suggested, which is put both packs in series and then hook the 2 packs in parallel? I will have a guy from radio shack who has years of running arduino and circuits. He is the only expert I know. He has even built a 3d printer with the arduino. \$\endgroup\$
    – Sean.D
    Feb 22, 2017 at 16:33

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