I need to record two tracks from two lavaliere mics for a very long period of time (days). So I want to connect a recorder to portable charger via usb. Audio quality is not extremely critical to me. What recorder should I use?

I've been looking at Zoom H4n / Zoom H4n Pro but I'm confused about two things:

  1. Is it able to charge batteries while recording?
  2. Is it possible to record sound from two lavaliere mics into separate channels (files)?

Any other options I should consider? Theoretically I'm even okay with buying two one-channel recorders. I have one Zoom H1 now but it is not able to charge batteries on the go.

  • Do you intend to record continuously for days ?
    – audionuma
    Commented Mar 13, 2017 at 6:48
  • @audionuma, yes. Usually about 15-24 hours Commented Mar 13, 2017 at 9:52

3 Answers 3


"Recharging on the go" sounds like you have a power outlet available. Why not just let the Zoom run on its power adapter rather than batteries?

  • My "power outlet" is a portable usb battery in my backpack Commented Mar 13, 2017 at 17:53

A "portable USB charger" will likely deliver 5V. If that's what your Zoom takes, you can just power the Zoom with the "USB charger" given a suitable cable to the power connector instead of doing any actual charging.


There are two main issues to consider when dealing with your project :

  • recording duration

  • power supply

Let's say you want to record continuous 24 hours audio on two tracks and that every 24 hours you can stop recording for a few minutes to change recording medium and power supply.

Recording duration

Although you mention that

Audio quality is not extremely critical

I will suggest to record in PCM format at 44.1 KHz or 48 KHz sampling frequency. This implies that a .wav file cannot handle such duration as it has a file size limit that is under your needs.

24 hours stereo 16 bits in 48 KHz is a little under 16 Gb.

Fortunately, many recorders have a functionality that will split the recording in several files if the file size grows over the format limit. It means that recording 24 hours will leave you with several files that you need to concatenate to obtain the full duration. It seems that zoom H4n and H4n pro offer this functionality. You need to check that by yourself as I couldn't find a definitive answer in the product's guide.

So, you need a 32 Gb recording medium to be on the safe zone.

Power Supply

The external power supply available for zoom recorders mentions 5 V / 1 A. If a power plug is present, use the external power supply. If it is not, for 24 hours recording without interruption it would require a power supply of 5 V voltage with approximately a 24 A.h charge. (And you would need one of these for each 24 hours time slice).

Notice that the nominal charge of a given accumulator may vary a lot depending on the technology used and the actual temperature. (I mention that because of the siberian mention on your name, in cold temperature, expect a much lower capacity than nominal one).

  • One of the reasons why I'm not sure about H4n (besides lack of the ability to power it via USB) is high energy consumption. Hopefully basic audio recorders consume much less energy (and I'm ready to have two small recorders instead of one big one). The problem is to find a recorder that is capable of doing what I need Commented Mar 13, 2017 at 21:12

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