Battery monitor/Alarm

Morning All
Looking for advice on the voltage monitoring and use of 4200maHr LiFe battery’s please?

What are the lower limits for these types of battery, and what are people using to warn when getting near the limit please?

I have been using a couple of 5200 Lipo with a monitor that plugs into the balance socket - struggling to find a LiFe version of the same.

Any pointers appreciated.



I use an FT817 and have the display set to show the battery voltage, frequency, mode and SWR. I just keep an eye on the display and stop when it drops to 11.5V.

I use the same battery type and capacity, and I keep an eye on it as Andy does, with the FT817 meter.
Having said that, the nearest I have come to running it low so far is 2.5 hours of UKAC, running the 817 and an SG Labs transverter. Even then, it only takes about 3 AH of charge afterwards, so a good safety margin.

I would quite like to add some sort of monitoring device that would alert me, though, as the batteries can be easily damaged by over discharge - so I’ll watch this thread with interest.

I used to use an alarm but found that a Watts Up or similar that shows you the amount of Ah drawn from the battery a better way.

Here is an example, there are thousand of them to chose from. And yes, they are made in China as is most of your radio…

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I have an alarm which may be similar to the one you used for LIPOs, it has a button that can reconfigure the alarm voltage from 3.2, 3.1, 3.0 all the way to 2.5 from memory. So it can be used for either LIPO or LIFEPO4 battery types.

It plugs into the balance lead socket. I think the left button when pressed displays the alarm voltage and keeping it pressed, or pressing again, lowers the alarm voltage, so by cycling around you can move it from 2.x to 2.y. Ie whatever you need.

Andrew VK1DA/VK2UH

Absolutely essential if you do not want to goose your battery by discharging too far. I use one in my model boats as well and it can be heard from around 100 m.
Don’t do what I did though, leave it attached and the battery in the bedroom - xyl was far from pleased when it went off at 3 am :frowning:


Yes, they do draw a small amount of power so in time they will flatten a battery plus set themselves off. Mine didnt go off in the bedroom fortunately!

Great thing about me Yeasu 450 and the 857D is if they drop below 11v they switch off. I know then battery is getting lowish on my slab and Lifopo4’s :slight_smile:

I abuse the heck out of my LiFeP04 packs and have taken them down to 10v… but they were free so…


Careful - the 857 at least draws phantom power for the front display and if you leave a battery connected to one even in the off state, the battery will drain. Don’t ask me how I know this.

Thanks for the advice all - Looking into the options and will let you know how I get on.

Hobby King are recommending this for the 4s1p LiFepo, although the product was designed for Lipo, as it is programmable they say it will also work with LiFepo.
I have a couple on order and will try them with a voltage meter for backup.
Postage was more than the product!


I have been using the LiPo voltage checkers on my RC models for years. When the alarm goes off…you land. Simple. The added benefit is you can see each individual cell voltage and it alarms as soon as any of the individual cells drain to the set voltage. They work very well. You can set the alarm voltage to whatever you like as stated above. They are also very cheap on Ebay. Well spent insurance money in my opinion.
Tim - K5DEZ

Hi Tim

Does this remember the voltage setting between uses? One of the reviews (not that reviews are generally to be believed…) suggest that the setting may be volatile when disconnected, which would be a tad inconvenient - though not as inconvenient as knackering your batteries :wink:

73 de Paul G4MD

The ones I was using always kept the settings. (They look just like the one pictured above) I do not know all and see all …but… I have not seen one that loses the settings. For as cheap in price as they are you would not be out much money…worth a try for sure.
Tim - K5DEZ

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That’s great Tim many thanks for the feedback I’ll give 'em a go :slight_smile:

73 de Paul G4MD

I can confirm that these do retain their settings, they can be set to “OFF” or to alarm at 2.7V - 3.8V, They’re non-latching, so if one cell dips temporarily below the alarm point when it rises above the set voltage again the alarm stops.

Also they are LOUD :slight_smile:

Edit: Based on a sample of one, on a fully-charged 4S LiFePO4 battery the current drain was an average of 16mA so shouldn’t impact too greatly on the run-time obtained from a 4200mAhr unit!

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Hi Paul - are the LEDs illuminated all the time, or is that in some way optional?

Hi Adrian,

There’s only one LED, a red one, and it only flashes in the alarm condition. It’s tucked between the display and the sounders, so may not be particularly visible in some conditions, although it is quite bright. The three-digit seven segment display continuously cycles between individual cell voltages and total voltage.

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Thanks Paul,
Just had notification my Hobbyking shipment has been delayed - hopefully here Tuesday and I can test them out.