Battery power supplies for the Regen

[Cornan]

Hi John!

I own the KingRex uPower myself and use it to power the USB Regen. There is two things that have haunted my mind lately and I cannot really find a good answers online. If you have any knowledge about this I would appreciate some advice!

 

1. Battery supplies are sensitive to ground and tend to store the current in the chassi. Would it ve a good idea to ground the chassi to an external grounding point like Entreq Minimus?

 

2. I know that batteries just store energy from chemical reaction and in my "sensible mind" the power charging the batteries will not make any difference. My "mad scientist mind" say that the mains noises should penitrate the batteries and will make a difference with a "cleaner" output battery power...so using linear power (or even battery power charging the battery) should increase battery performance to the supplied SPMS. Which part of my mind is speaking the truth?

 

/Micael

[Cornan]

I'm really enjoying my stock Regen, but would love to squeeze more performance out of it on a modest budget. At Alex's suggestion, I thought I'd start this thread for folks who are powering their Regens with batteries or would like to—both commercial products like the Kingrex Upower and also DYI.

 

I, for one, would love to find an inexpensive battery solution without spending hundreds of dollars. Several users here have commented that inexpensive lithium ion batteries on Amazon can be made to work pretty much off the shelf, and can provide better SQ than, for example, the "El Cheapo" Chinese LPS.

 

Anyone care to share their experiences, photos, and listening impressions?

I think you might want to check this out http:// http://www.head-fi.org/t/762967/uptone-audio-usb-regen/960_40

Michael (from Elijah Audio) have promised to report back on SQ on his cheap battery solution for USB Regen.

[Cornan]

Cornan

You have completely lost me with point 1.

It doesn't make much sense to me.

Yes, charging a battery while in use will result in noise modulating the battery power to some extent.

Even several banks in parallel of 24 series 2.2V 2,200 AH (or higher) batteries in a Telephone Exchange can't completely silence the effects of the huge rectifier cabinets that "float" them. As usual, it depends on the quality of the charging apparatus and the filtering of it's output. I use either a low noise Linear PSU followed by a Super Regulator, or a 12V 4,000mAH Li Ion rechargeable battery regulated down to +9V followed by a "Shunt" type of Super Regulator. This slightly outperforms the Linear PSU when powering the Regen, due to the capacitive coupling between Primary and Secondary sides of the transformer back to mains earth, which results in a minor earth loop.

 

Alex

 

Thanks Sandyk! :-)

However, my question was if the battery power itself will be cleaner if charged by a linear PSU than a SPMS for example, ie. If the battery power without a connection to the mains will be cleaner if been charged by LPS than with SPMS.

 

On my point 1 I have already got an answer of my question. I e-mailed to Entreq to know if it was safe to ground my KingRex uPower

 

 

thought the Entreq Eartha USB cable

 

 

to my Entreq Minimus grounding box http://www.entreq.com/products/ground-boxes-17667704 . The answer was yes and I recently hooked it up. Without saying too much (since this will be improved during the Next 24hrs) the results exceeded my expectation with blacker and more noise free back ground...so I am happy and are expecting to be happier tomorrow! :-)

 

/Micael

[Cornan]

So you are asking if the quality of the power that charged your battery (and was then disconnected) results in different quality of the power delivered by said battery. Uh no offense, but that seems as likely as my typed words having more emphasis if I hit the keyboards keys harder.

I'm no stranger to odd things--heck the entire operating principal of the REGEN was considered odd or ridiculous to many (still is to some) when it first came out--but it would be a long time before I'd buy into the notion that the chemicals of a battery form and discharge differently depending upon the noise and spectra of what charged them.

 

Have a great weekend all.

 

--Alex C.

 

Thanks Alex! As I said in my original post this does'nt really make sense to me either...but my crazy scientist mind just had to ask. In a way AC currents is forcing itself into unimaginary places...forwards and backward etc. It would'nt surprice me if the currents is mixed in the chemical reaction and affecting the DC output...even if the sensible me says no way! ?

 

Have a nice weekend! [emoji4]

[Cornan]

Hi Cornan

 

Superdad beat me to it.

BTW, it's always best to completely remove the charger, whether SMPS, or a Linear PSU, while playing music, unless you are using a supply like the soon to be released Uptone Ultracap supply which according to it's designer John Swenson, completely isolates the supply from the mains, However, it can't stop crap getting back into the A.C. Mains sewer from an SMPS plugpack, and to a far lesser extent from a well designed Linear PSU.

 

 

That seems highly unlikely, even if you are using unfiltered rectified D.C .

A typical SMPS has a reasonably low ripple output and the high equivalent capacitance of the battery itself should take care of that very small residual, just as a large value low ESR electrolytic capacitor at it's output would.

 

 

 

Alex K.

 

Thanks Alex K!

I always play music unconnected to the mains with my uPower and charge when ever not listening to music to save the battery cycles. KingRex uPower shuts of the charging when the battery is fully charged so I do not need to monitoring it.

 

A new morning and I had to take a new listen to my externally grounded battery. I am so happy I thought of this and did it all though I could'nt find anyone else with this idea online. Passengers album "Whispers" sounds better than ever with tons of depth and details...and last but not least dig out the music soul and gives my shivers of joy. My Aurelic Aries Mini is also grounded via the Spdif output BTW...so the battery is not the only thing grounded and play a part of this improvement as well of course. I think I will have start saving for another Minimus and two Eartha cables. I want to ground my router and my coming 16,8v battery supply for my Aries Mini as well.

 

I guess the LPS for improving battery cell performance is a dead-end...but I am happy I asked. Thanks!

 

/Micael

[Cornan]

Here is some pictures of my rig if someone is interested to see how the setup is done!

 

 

 

[Cornan]

Nice set-up Cornan! That ceramic tile looks like just what we just remodeled our guest bathroom with.

Thanks Alex! *Haha* no that is made of plastic and is a wireless charger for my 7" Android tablet that I use to control my music (BubbleDS Next control point). I love that charger!

[Cornan]

Here is another picture that might make it more clear how my little audio corner looks like! ?

 

[Cornan]

@Alex It just occured to me that you ment the grey Italian tiles under my Aries Mini and Pioneer u-05. These were left overs from our bathroom renovation. We had them both on the walls and on the floor with real valnut cabinet. I was extremely happy with that renovation! ?

[Cornan]

It just strucked me that there is actually a good way to find out if the battery cell performance could be affected by incoming DC power quality. In any case I have been interested to try out the iFi DC iPurifier Accessory – DC iPurifier with my uPower pre DC input to my USB Regen. I could actually use it pre DC input of my uPower as well to see if there will be any noticable changes what so ever in the sound unconnected to the main if charged with the DC iPurifier in line. If no change in SQ I will still have use for it in the other end. Could actually be a fun test!

[Cornan]

After some searching I have found a suitable battery pack for USB Regen for USD39,95 Lithium Ion Battery 7.4V 4400mAh

 

 

If you add this T-connector male to DC5.5/2.1mm DC plug for USD3,90 Male Dean (T-connector) to male 2.1mmx5.5mm DC barrel plug cable:Tools & Accessories,Cables - FPV Model: RC Plane, Multicopter, Quadcopter, FPV Goggles, FPV System and all things FPV.

 

 

you should have a pretty good & valuable battery pack for the USB Regen without soldering skills or the hassle of buying from China!

[Cornan]

Thanks Cornan! How long do you think this pack would hold a charge with the Regen? Can it operate (and sound good) while plugged in to the AC adapter?

 

You are welcome mink70!

The answer of you questions depends if your DAC is USB powered or not. If your DAC requires USB power I guess this battery will last at around 4-5 hours playtime. On the other hand if your DAC does´nt require USB power it will most likely run for arund 24 hours.

I do not recommend to use any battery connected to mains while playing music. Even if it was isolated from the mains (which it is´nt) like my uPower it still sounds better when unconnected from the mains. However, since this battery have a separate lead for the charger and have a charger with over-voltage protection and under-voltage protection it will be ok to charge it at the same time as powering the USB Regen. You should however understand that the cut-off voltage on this battery pack is set to 5,5V which means that when the battery reaches 5,5v the DC power is cut-off. If you have a USB powered DAC you´ll need to ask @Superdad if the voltage will be enough...otherwise you´ll need to make sure to stop listening and charge it before it cuts off. Hope that helps!

[Cornan]

Thanks Cornan and John! I really appreciate the links!

 

Since John built the Regen, I'm going to rely on his more optimistic 88 hour estimate

 

You are welcome! Yes, of course you must trust JS! I was just extremely modest with my estimation...afraid to give you too high hopes! Anyway, here is a handy tool if you want to calculate the battery life yourself Battery Life Calculator | DigiKey Electronics

[Cornan]

No, it won't be O.K. for best results.

The USB Regen should be if possible, powered from a source that has no connection to the A.C. mains, and hence some degree of an earth loop. John has already stated that the power source should be unplugged from the battery when playing.

That is what I wrote in my reply as well. This part of the reply is just me explaining that it is safe to charge while the USB Regen is connected.

[Cornan]

You mentioned that the output voltage is cut off when the battery voltage drops down to 5.5V, but you haven't mentioned what the over voltage limit is. Obviously the charger's output voltage will need to somewhat over 7.2V to fully charge a 7.2V battery.

Personally, I wouldn't rely on a charger's over voltage limiter to protect something like a Regen.

If you really need to use the Regen while the battery is charging, it's better to buy 2 batteries that you can use alternately.

 

The over-voltage limit on this battery pack is 8,4V so it will perfectly safe.

 

IMO, the whole point of getting a battery pack with charger is that you can avoid constant battery changes. Ohwerwise it is very easy to just buy THIS

 

 

and THIS

 

 

and be done with it. However, that would mean contant monitoring of both high.voltage AND low-voltage plus the hassle of changing a pair of 18650´s while charging the other pair. I would personally prefer a battery pack with charger and day.

 

BTW. The battery pack is 7,4v...not 7,2v.

[Cornan]

Here is a good & easy to read link if you want to know the high-voltage vs low-voltage on a standard 3,7v Li-ion 18650: https://learn.adafruit.com/li-ion-and-lipoly-batteries/voltages

 

What this link tells you is that the nominal voltage of a 3,7v Li-ion with 2pcs in series (=2P2S) will be 7,4v, the low-voltage will be 6v and the high-voltage will be 8,4v. With 2P2S configuration the amperage will be the same as in a single battery. In my example above (post #27) 2pcs 3,7v/5300mAh batteries will give you 5,3A in a 2P2S configuration, will have a nominal voltage of 7,4v, will never drop below 6v (unless the battery cells gets damaged or fully discharged) and will never go higher than 8,4v (since it is not connected to a charger). Nothing of that will damage the USB Regen.

 

The low-voltage cut-off (5,5v) on the earlier posted 7,4v battery pack is just a precaution for battery cells damage and battery discharge and the high-voltage cut-off (8,4v) is just a precation when the battery is connected to a device to ensure that the charging voltage peaks do not exceed the maximum 8,4v which could damage the connected device.

 

I think I got the most important things covered there. If not please let me know!

[Cornan]

Cornan

There are just as many Li Ion batteries listed as 7.2V. If you do some research you will find that the basic voltage is actually 3.65V with 2 in series . 7.4V sounds more impressive than 7.2V though doesn't it, when it is actually more like 7.3V ?

This is like with a "9V" Ni MH battery where the actual voltage is more like 8.4V.

 

 

Battery Voltage Information – Battery University

 

Thanks for that Sandyk! I have actually read this page before...but that detail did´nt stick to my mind. Now it have. You live and you learn!

 

/Micael

[Cornan]

Has any one tried a 5V Bakoon BPS-02?

Bakoon BPS-02 (5v), Kingrex uPower (7,5v), SOtM mBPS-d2s (9v) & Kingrex SLAP (12v) are some of the most interesting battery supplies around. The only one that works with USB Regen with or without USB powered DAC is the uPower. If your DAC do not require USB power (or handshake) you can choose which ever one you like. LPS-1 will work with all of them except BPS-02 but it would be an over-kill to choose any other than uPower.

I have'nt tried BPS-02...but have always wanted to!

[Cornan]

Here are pictures and links to all the mensioned batteries...just save you some valuable Google-time!

 

Kingrex SLAP! http://www.kingrex.com/products.php?c=6&s=9

 

 

Bakoon BPS-02 BPS-02 - Bakoon International Corp. (discontinued but still available at some local dealers)

 

 

SOtM mBPS-d2s SOtM - English | mBPS-d2s

 

Kingrex uPower http://www.kingrex.com/products.php?c=6&s=14

 

 

Here is a link to the CA thread for the coming Ultracap LPS-1 if someone have missed it: http://www.computeraudiophile.com/f27-uptone-audio-sponsored/mystery-revealed-uptone-audio-ultracap%99-linear-power-supply-1-a-28609/

[Cornan]

i used the SOtM battery PS with the REGEN and it worked just fine. I'm using it now with the Sonore microRendu and it works well with that too.

Thanks Guodof! Reading about the SOtM again I realize that I got the specs wrong. It can deliver 6,5~8,4v not 9v. Should indeed be the perfect choise for USB Regen, microRendu and LPS-1.

[Cornan]

I think the SOtM battery is short in terms of the current required to energize the forthcoming LPS-1.

 

At the 6 to 9vdc output range of the SOtM battery, the LPS-1 will require between 2 - 2.5 amps of current, the SOtM battery only outputs 1.5 amps.

 

The SOtM battery specs:

 

Power output : 5.5mm x 2.5mm DC jack

- Battery output voltage : 6.5Vdc ~ 8.4Vdc

- Output voltage Range : 6Vdc ~ 9Vdc

- Current : 1.5 A

 

The low input voltage for the LPS-1 is stated as 7.5v, so that too looks like a bad match for the SOtM battery which will likely sag below that to 6 or 6.5v as it discharges.

 

Thanks MikeyFresh! Well, then it seems like my KingRex uPower with 7,5v/2,6A is not only the cheapest (approx GBP 150) but safest bet among the mensioned BPS for the Ultracap LPS-1...as long as you run it completely unconnected from the mains.

 

Bakoon have the same current as SOtM and KingRex SLAP! have voltage peaks up to 14v (LPS-1=max 12v).

[Cornan]

Hi Cornan,

 

 

 

There's a potential problem with the PCM-equipped 7.4V battery pack linked, above. On the specifications page, it indicates that the built-in PCM (Protection Circuit Module) has a discharge cutoff voltage of 5.5V. That's obviously not the cut-off voltage for individual cells, as they will measure 4.2V when fully charged, so it's the cut-off voltage for the entire pack.

 

Problem: This is a 2S2P pack, so if the PCM is not going to stop the pack from discharging into a load until the sum of two cells in series is 5.5V, each cell could fall to an average of 2.75V per cell.

 

If a user allows this to happen, by nature of trusting the PCM instead of monitoring the voltage on his own to stop using the pack when it reaches 6.6V (3.3V per cell), having discharged from a maximum voltage of 8.4V (4.2V per cell), individual cells could go into phase reversal, suffering permanent damage, with the possibility of spontaneous combustion (not necessarily an explosion), but a fire just the same, with toxic soot getting spread about. Call a hazmat crew after you put out the fire. :-)

 

Ironically, at the top of main page for that same battery pack, the following warning is given:

 

 

 

Do you see the disparity? They smartly warn us not to allow any one cell to drop below 3.3V - which is pretty much a standard warning for all LiPo batteries, although some people will say that 3.0V is the absolutely lowest you can go - and yet, going by the specifications, they contradict themselves by using a PCM that will allow a two-cell series voltage to fall to 5.5V (2.75V per cell) before it will shutdown.

 

I ruined a $100 6S LiPo pack once, by pushing the discharge all the way down to 3.0V per cell on each discharge cycle - and I was monitoring individual cell voltages during use, with an audible alarm that was set to go off if any one cell hit 3.0. The battery had only been cycled perhaps 7 or times, when a cell that had repeatedly reached 3.0V ahead of its siblings, decided to stop taking a charge. The pack started swelling when I put it on the charger. That was the end of that pack. So now, I stick to a 3.3V minimum per cell, religiously.

 

Unfortunately, the pack pictured above can't be monitored on a cell by cell basis, because it's not wired for a balanced charger. Both of its connectors use two-conductor connectors. A load only needs two conductors, of course, but the pictured "dumb" charger will charge each of the two banks of series-wired cells, together as a unit, not independently as a balanced charger would. So, there's yet another weakness built-in to this battery pack. Over time, in either one half of the pack or the other or in both halves, one cell in a series pair, could begin to exhibit a higher resistance to the charge current, such that by the time the two cells, together as a unit, reach the PCM-governed charge cut-off voltage of 8.4V, the stronger cell can actually be forced to exceed the safe maximum of 4.2V per cell - you'll be cooking that cell - while the weaker cell in a series pair is left behind at something less than 4.2V per cell.

 

Then, during repeated discharge/charge cycles, a snowball effect can take place, as the weaker cell is always sucked down to a lower voltage than its stronger sibling, leaving it all the more vulnerable to suffering damage from going below 3.3V while the other cell is still putting out something greater than that. (And that would be worse if you and/or the PCM allow the total voltage of the 2S pack to drop down to 5.5V before shutting it down.)

 

The fact that this battery pack is not wired for balanced charging is only compounded by the fact that its PCM allows the voltage of the pack as a whole to drop down to 5.5V. The two "oversights" will work together to shorten the useful life of the battery. Assuming the manufacturer actually knows what they're doing and that there are no errors in the published specifications, I would have to conclude that this pack is designed to fail after only a couple of dozen charge cycles - so that you'll toss it and buy another.

 

A battery pack wired for balance charging will have a two-conductor cable for discharging into a load, just like this battery pack, but it will have a JST connector for charging - similar to a small Molex connector, that has one conductor for each cell in the pack, plus a common ground wire. PCMs do not balance charge a pack internally, so the only way to keep the cells nicely matched throughout many usage cycles (500+), is to buy a balance charger and a battery pack that's made for balance charging.

 

That same vendor sells this 7.4V 4500 mAH 2S1P LiPo pack that's wired for balance charging (or monitoring the voltages of each cell during discharge through the separate two-conductor cable):

 

[ATTACH=CONFIG]26745[/ATTACH]

Tiger 7.4V 4500 MAH 30C LiPo Battery with T Plug

 

 

This photo shows a close-up of its JST connector - used for charging:

 

[ATTACH=CONFIG]26746[/ATTACH]

 

Three wires, not two - allowing each cell to be charged or monitored independently.

 

Here's an affordable ($16) balance charger for that pack:

 

[ATTACH=CONFIG]26747[/ATTACH] [ATTACH=CONFIG]26748[/ATTACH]

Balance Charger for 7.4-11.1V 2-3S Cell Li-Po Battery

 

And here's a LiPo voltage alarm that I've used for several years (to monitor the aforementioned 6S packs I use to power a 24V TBI Millinea MG3 speaker amp for near-field monitors):

 

[ATTACH=CONFIG]26749[/ATTACH]

1-8S LiPo Battery Voltage Tester/Monitor

 

Just press the JST connector of a 7.4V, 2S pack onto the first three pins and it will start cycling through the cells to show the voltage of each, then the total voltage of the pack. In my experience, this alarm doesn't put any noise at all into your audio signal. (Which begs the question: How silent is a PCM that's equipped with a current-limiter?) You could leave it disconnected during play, re-attaching it occasionally throughout the discharge cycle, but that kind of defeats the purpose. Another feature of this alarm is that there's a little button which allows you to adjust the per-cell voltage at which it will alarm. I use do have mine set at 3.0V, but now I leave it at 3.3V. By the way, those little tweeter horns are ear-splittingly loud. They can be heard from the ground when mounted inside an airborne RC airplane or helicopter. I stuffed mine with some Play-Doh - I can still hear them when listening to music. :-)

 

Speaking of current limiting, this balance-wired battery pack, as with most of its kind, has no PCM and thus, has no current limiter. The specifications page for this battery says it has a maximum continuous discharge rating of 30C. A "C" rating can be converted to Amps (not milliamps) by dividing the pack's mAH rating by 1000, then multiply by the C rating.

 

So, for this 4500 mAh pack, with a 30C rating, we get (4500 / 1000) * 30 = 135 Amps. No kidding! This LiPo pack can deliver a continuous current of 135 Amps, without overheating, until it is fully discharged (3.3V per cell), in roughly 2 minutes flat.) That's why they are used by RC racing hobbyists. (Don't short the wires!)

 

Do we need a current limiter for use with DC audio gear? Without naming names, I've been told by three different manufacturers that their DC-powered audio gear will not pull more current than it can use and that it's safe to use my RC LiPo batteries without a current limiter, but one of them joked that any dust bunnies that might fall across exposed power terminals could cause a momentary arc. Arcs across clean air require much higher voltages, even for short distances. :-)

 

I've used unlimited LiPo packs with multiple pieces of audio gear for several years - never having any problem related to their ability to dump a lot of current. But if you want to shop for larger capacity 7.4V LiPo packs that are wired for a balance charger, I would try to stick with 15C, 20C, 25C, or 30C. The really big packs can go as high as 65C.

 

Here's a brand of LiPo pack I like: GensAceUSA - High Performance LiPoly (Lithium Polymer) Batteries for RC Cars, Helicopters, Planes, Boats, Trucks, Crawlers

 

Mike

 

Hi Mike!

 

Thanks for that awesome lecture!

I am currently on holiday in Torrevieja/Spain and cannot answer in details. All I know is that Lithium ion battery packs (it is not a LiPo brw) like the one I posted (with charger) cannot be sold without voltage regulators. I know that cautions posted by resellers and manufacturers are likely just precautions not to be sued by consumers. If you read about this battery pack sold in the US you will find this info as well:

If discharged too low, Lithium Ion batteries can become unstable and unsafe to use. However these battery packs have built in under-voltage protection. This means that when they fall below the cut-off voltage, the batteries will turn off, preventing the Lithium Ion cells from discharging too low. protecting your battery.

 

The included battery charger and over-volt protection ensure that the battery is charged at correct voltage levels. The charger will change its LED from red to green when the charging process is done.

 

This makes sure that the battery will not burn, smoke etc. However, with batteries it is always best to be safe. Buy it locally and ask the reseller about the limitations and how to use it properly. Btw, I think this should be a 1s4p just looking at it. 2s2p is normally bulked in pairs. Now, back to sunny Torrevieja!

 

/Micael

[Cornan]

Good idea! You can ignore the annotations I added to this photo when reviewing the Audiophonics PCM5102 DAC, but it shows a similar meter I hobbled together in the absence of good soldering skills. (I practice DIY for Dummies.)

 

 

With both male and female 5.5mm connectors, it's pretty versatile.

 

https://www.amazon.com/gp/product/B00JOB793W

 

https://www.amazon.com/gp/product/B011YKCK5M

 

https://www.amazon.com/gp/product/B00H0GVYMA

 

Battery hounds love these, too:

 

https://www.amazon.com/gp/product/B00ORGDQOK

 

I love this voltage meter Mike! I have been looking for something like this ready made all over without success.

I wonder if it would be possible with a similar idea for cut-off voltage? Something with swapable voltage regulators (say 6v, 9v, 12v & 14v) would be a brilliant idea for anyone with a business mind! I would buy it instantly!

[Cornan]

Hi Micael,

 

First, first let me say that Li-Ion and LiPo have the same chemistry, the only difference being that LiPo (Lithium Ion Polymer) refers to Lithium Ion batteries where each cell is in a polymer sleeve (as with the RC batteries I use). When they are cylindrical, like the 4-cell pack you are referencing, they should be called Li-Ion, not LiPo. So, I had not used the proper terminology when I referred to those Li-Ion cells as LiPo, but they have the exact same chemistry, the same risk of fire if abused, the same minimum and maximum cell voltages, etc.

 

Have another look at the large print on this page: Lithium Ion Battery 7.4V 4400mAh

 

That pack is a 2S2P, not a 1S4P. If it were a 1S4P, its nominal voltage would be 3.7V, not 7.4V.

 

Quoting my earlier post:

 

 

 

Search the web high and low - you will not find anyone advising you to discharge Li-Ion (or LiPo) cells down to voltages below 3.0V, so the published specs for this pack are incorrect -or- the pack should be avoided. As I previously shared, even allowing cells to fall all the way to the recommended 3.0V minimum can leave you having to soon replace a pack.

 

:-)

 

Mike

 

I hear you...and surrender to superiour battery knowledge! I would'nt be too afraid to drain that battery pack though. As John S mensioned it would a last very long time (longer than any sensible listening session) and I would personally charge it after each use (not when drained). It would not be even close to damage any of the cells if done this way with the Regen. You are right though to get peoples attension about the possible problems that could occur if not being careful about it!

[Cornan]

A couple of $ will get you one of the attached or similar , which are available in different LED colours ( I have a couple with White LEDS )

DC 0 100V 3 30V Digital LED CAR Voltmeter Gauge Voltage Panel Meter 2 3 Wire PRO | eBay

They are also available from quite a few other ebay suppliers such as

Bang good.com which has many other interesting gadgets too.

led volt meters - Buy Cheap led volt meters - From Banggood

They only draw about 20mA from the battery, so they won't shorten the listening time by much with a larger AH battery.

 

Thanks Alex! I will certainly look into this for my coming 16,8-12v battery pack for my Aries Mini which I'll need to monitor so it does'nt go under 14v.