LifePO Batteries Explained

LifePO4cell Batteries

UPDATE : Since writing this post, my batteries (an 8.4Ah and 4.8Ah) are approaching their 4th birthdays. They have been 100% trouble-free and I've been incredibly happy with my purchase. I've mainly used the 8.4Ah for my longer outings and the smaller one for more local work. I have used them with Elecraft KX3, Icom IC-7100, Yaesu FT-818 and more recently with my Icom IC-705. The big battery seems almost impossible to drain!! HIGHLY RECOMMENDED!

When I bought a couple of LifePO4 “ZIPPY FLIGHTMAX” batteries from HobbyKing to power my radios while out and about, they arrived with zero information about how to look after them. No advice on how to use them, charge them, maintain them or store them. I was aware that they could be dangerous and that they had specific charging requirements in order to prolong their life. So, after spending ages trawling the internet, I've learned a bit. Hope others find it useful. 

Rechargeable Li-ion, Li-Poly and Lithium Iron Phosphate (LiFePO4) batteries differ from the standard Lithium batteries in that the latter are not rechargeable. The lithium-ion batteries Li-Ion usually have a nominal voltage of 3.6V or 3.7V., The LiFePO4 have a nominal voltage of about 3.2V or 3.3V and the lithium-polymer Li-Po batteries have a nominal voltage of 3.6V per cell. With Li-ion and LiPo batteries the recommended per-cell safety zone is usually between 3V (fully discharged) and 4.2V (fully charged), although they can normally discharge down to about 2.8V without any problems. 

Discharging below that level may cause irreversible/irreparable damage. Therefore, these batteries often feature a built-in safety mechanisms, preventing over-discharging. 

Conversely, overcharging can also be dangerous. The Li-Po batteries have lower number of recharging cycles than LiFePo4 (1000@0.2C rate, IEC Standard). The projected/estimated life of a Lithium-Ion battery is approximately 3 years from production. 

The LiFePO4 batteries exhibit slightly different properties: They have a bit lower operating voltage of about 3.2V – 3.3V, the minimum discharge voltage is 2.8V and the maximum charged voltage is 3.6V. The LiFePO4 is a kind of Li-Ion rechargeable battery intended for high power applications, such as EV cars , eBikes, electric bike, Power Tools, RC or HAM Radio. 

The LiFePO4 batteries have more constant discharge voltage and are considered to offer better safety than other Lithium-based batteries. Other advantages of the Lithium-based rechargeable batteries include the ability of a much faster recharge and higher discharge rates than other chemistries mentioned and usually higher number of recharge cycles (>2000@0.2C rate, IEC Standard) , meaning longer life when not fully discharged, but its energy density is lower than normal Li-Ion cell (Li-Co). LiFePO4 life expectancy is approximately 5-7 years. 

The S’s: 

A single LiPo cell has a nominal voltage of 3.6 volts. Since battery packs come in different sizes and voltages, it is more convenient to denote the voltages by saying 10S rather than 36 volts. To find out the nominal voltage of any pack, take the number before the S and multiply it by 3.6. This will render the voltage for the pack. So, a 13S pack will have a nominal voltage of 46.8 volts. 

A single LiFePO4 cell has a nominal voltage of 3.3 volts. Since battery come in all sizes, it is more convenient to denote the voltages by saying 12S rather than 36 volts. To find out the nominal voltage of any pack, take the number before the S and multiply it by 3.3. This will give you the voltage for the pack. So a 16S pack will have a nominal voltage of 52.8 volts 

The P’s: 

To increase the capacity of the battery pack, additional LiPo cells can be added in parallel to keep the voltage constant while doubling the capacity. Let us take an example of a 10S LiPo with a total capacity of 2000mAh. Now, to get 4000mAh, we have to take another 10S/2000mAh pack and wire it parallel to the first pack. This would then be denoted by 10S2P, where the P indicates how many 10S packs there are in that battery. 

Ah: The capacity of the battery pack is stated as a rate rather than a quantity. 10Ah means that it will take a 10A load an hour to drain that pack. So if we applied a 20A load to the pack, it would be drained in half an hour, disregarding internal losses and such. To make a pack last longer, one may want one with a large Ah number. 

One could also increase the available capacity by taking two identical LiPo and wire the leads in parallel, positive to positive and negative to negative, before connecting it to their appliance. That would double the capacity while maintaining the voltage. If we wired the leads in series, one positive lead of battery 1 to one negative lead of battery 2, we would end up with twice the voltage at the same capacity. This is useful when we only have 5S batteries at hand and a 10S battery is needed. When combining batteries, the participating batteries must all be identical in voltage and capacity. 

C Ratings:

The first set of C ratings on a LiPo tells us how fast the battery can be discharged. 20C/30C translates to (maximum constant discharge rate) / (Burst discharge rate). Burst can last for up to about 10 seconds. To figure out how many amps this rate is, you need to know the capacity of the battery pack. If the pack says that it has 10Ah, take that number before the Ah to get the number of amps. In this case, it would be 10. 

That is your rating of 1C for that pack. Therefore, if the pack says it can safely continuously discharge at 20C, then that means it can supply a constant 100 amps of current. The burst rate would then be 200 amps for 10 seconds. The smaller C rating following the first pair is the charge rate. LiPos must be charged at a much slower rate than its discharge rate. Most packs are good with up to 2C charge rate (for this example, it would be 20 amps). 

Charging - Discharging rates : 

To charge a LiPo pack, it is highly encouraged to use a charger that supports individual cell balancing or a charger and a battery pack with a BMS. This way, all the cells come off the charger at equal voltages so they all charge equally. When using that charger, you will notice that the charging current drops off as the pack nears its maximum charge, 4.2 volts for one Li-Po cell and 3.6V volts for one LiFePO4cell. This is done so the charger does not overcharge the cells which will cause a fire. Determined in the same fashion as the C ratings for discharge, the C rating for charge tells you at what amperage you can safely charge your battery. This information is generally listed on the back of the battery with all the safety information. For a 10 Ah battery, 2C means that it can be charged at 20A (2*10A). 

Proper Charging: 

It’s important to use a LiPo compatible charger for LiPos and LiFePO4 compatible charger for LiFePO4 batteries. They charge using a system called CC/CV charging. It stands for Constant Current / Constant Voltage. Basically, the charger will keep the current, or charge rate, constant until the battery reaches its peak voltage (4.2v/ 3,6V per cell in a battery pack). Then it will maintain that voltage, while reducing the current. On the other hand, NiMH and NiCd batteries charge best using a pulse charging method. 

Charging a LiPo / LiFePO4 battery in this way can have damaging effects, so it is important to use a LiPo / LiFePO4 compatible charger as appropriate. 

Internal Resistance ( IR): 

Internal Resistance is a measure of the difficulty a battery has delivering its energy to a motor and speed controller. The higher the number, the harder it is for the energy to reach its destination. The energy that doesn’t "go all the way" is lost as heat. So the internal resistance is a kind of a measure of the efficiency of the battery. However, there is a correlation between the C-Rating of a battery and the internal resistance of that battery. In general, batteries with a higher C-Rating also have a low internal resistance. 

As a general rule: 

· per cell rating between 0-6 mΩ is as good as new 
· Between 7 and 12 mΩ is reasonable 
· 12 to 20 mΩ is where the signs of lower capacity start to be observed 
· and beyond 20mΩ per cell, one may want to start thinking about retiring the battery pack 

BMS: 

A battery management system (BMS) is an electronic regulator that monitors and controls the charging and discharging of rechargeable batteries. The BMS comes included in battery pack. Battery management systems may be as simple as electronics to measure voltage and stop charging when the desired voltage is reached. At that point, they might shut down the power flow; in the event of irregular or dangerous conditions they might issue an alarm. 

A more complex BMS monitors many factors that affect battery life and performance as well as ensuring safe operation. They may monitor one-cell or multi-cell battery systems. Multi-cell systems may monitor and control conditions of individual cells. Some systems connect to computers for advanced monitoring, logging and more. A more complex BMS also monitors the temperature of a battery pack and can “cut-off” when the battery temperature is too high while charging or discharging. 

The small battery-tester above costs just a couple of £, so it's worth buying 2 or 3 so that you can keep one handy say in the garage, in your shack and in your go-pack. You simply connect it to your battery's Balance Connector and it will cycle through some figures...

. Overall battery voltage
. Cell-1 voltage
. Cell-2 voltage
. Cell-3 voltage
. Cell-4 voltage, etc

This is a convenient way to find out if your battery is not only charged, but also balanced! Just be aware that when you plug it in, there is a loud beep which will probably give you a bit of a fright, LOL.

Care: · 

A LiPo / Li-Ion cell should NEVER be discharged below 3.0V 

· A LiFePO4 cell should NEVER be discharged below 2.8V 
· Charge the battery pack fully after every use Storage: 
· Always store the batteries fully charged. 
· When not using the cell pack for an extended period of time, remove it from the appliance and store in a place with low humidity and low temperature 
· Inspect and Recharge the battery every few months 

UPDATE: Since posting this, I've had one person saying they should be stored at 50%, another said 70% and another at 80%. Clearly, the storage issue is as clear as mud and everyone has a different opinion. So decide for yourself. Personally I think I'll drop my LifePO4 to around 3.2V per cell if I'm not going to be using them for a while.

Please make a note of NIGEL BARKER's advice in the "Comments" section about these batteries being very much affected by temperature. The batteries don't like extremes of temperatures and you have to compensate for extreme variances. 

In high temperatures (forget the UK, LOL) you should probably drop the voltages of stored batteries. In freezing temperatures (yes, UK) the batteries may resist charging!

Safety: 

There are tons of safety precautions related to the use, storage, and disposal of Lithium Polymer batteries. Some safety precautions: Each one must be taken seriously since these high-power batteries will pack a punch when not used correctly. There are records of many things -from cars to entire houses - that have burnt down due to the misuse of LiPos. 

Never leave charging batteries unattended. If a battery goes wrong, you will have an incredibly intense chemical fire which produce massive amounts of smoke too. Google “Lipo Battery Fires”. I charge mine in a steel cabinet in the garage and each battery goes in a fireproof bag. LifePO are much more stable than Lipo but still need treating with respect – especially the bigger batteries! 

Never overcharge past 3.6 or 4.2 volts per cell. Over discharging will kill the pack. Drawing too much current from the pack can cause it to puff up and catch fire. Always use a proper BALANCE CHARGER like the Turnigy Accucell 6

REMEMBER:

1. Do not charge or use batteries if the battery ...
   1. is punctured or damaged
   2. is bloated, expanded, swelling or otherwise deformed
   3. has any cell with a voltage below recommended value
2. Do not charge batteries unattended. Monitor batteries during charging for popping, hissing, smoke, sparks or fire. Also monitor the battery for any swelling or other deformities. Disconnect the battery from your charger immediately.
3. Do not charge batteries near flammable material. Charge batteries in a fireproof container. Do not charge batteries while they are inside a device or inside a carry-case/rucksack.

Personally, I charge my batteries in my garage. I don't want to start being too paranoid about all this, but I do believe it's better to be safe than sorry! If (and it's a big if), a battery decided to go bad and catch fire, I want to be in a position where the fire can be contained and allowed to burn out without the risk of spreading and hurting someone.

So in my garage I have an old steel filing cabinet which I got from work (they were throwing it out). In the top drawer I place my batteries in their fireproof bags. Nothing else goes in that drawer!

I keep my charger on the outside of the cabinet and simply drop the charging lead into the top drawer.  IF a battery was to go bad during charging (or storage), the fire (it's actually a chemical fire - a very fierce one) would be contained within that safe area. 

Of course there would be extremely dense smoke billowing out, but there's nothing you can do about that, other than to let it escape through a wide-open garage door.

LET'S NOT BLOW ALL THIS OUT OF PROPORTION THOUGH because LifePO batteries are infinitely more safe and stable than the old Lipo batteries. And there's a large degree of sensationalism on YouTube driven by young lads who find it amusing to short them out for a firework display. 

Since writing this post, I have changed all power connectors to Anderson Pole connectors.

Great video by RC Model Reviews!

UPDATE : NOV 2021

I recently purchased an extra battery to use solely with my QRP-Labs QDX QRP Transceiver. It's a 7.4V 5500mAh Lipo with a balancer lead. This connects directly to my Turnigy Accucel 6 charger. I couldn't use either of my LifePO batteries because they're 13.2V and I needed 9V or less. The new Lipo has useful information written on the back of it stating very clearly that the cells should not be charged over 4.2V allowed to discharge lower than 3V.  For storage, it's best to have the voltage somewhere inbetween.

 

UPDATE : JAN 2022

I did something silly today - I left my battery connected to a Kenwood TS-2000 that I had borrowed and I took a phone call and got distracted. As a result, the radio drained the battery flat as a pancake!!

The end result was that my 8400mAh 13.2V LifePO battery had gone below the minimum acceptable voltage level and could no longer be charged - potentially junk!  😭

A tester revealed that two of the battery's cells were in a Fault state and the battery charger gave out a Battery Voltage Too Low warning and refused to charge. I decided that there was no use keep trying and so in desperation I changed the setting to NiMH and disconnected the Balance Lead.

With the charging current set to 2A, I started the charge and stood there watching the voltage of the battery slowly increase. There were occasions where it also started to go backwards briefly, but then it would get back on track and eventually reached 12.5V which meant that the cells were at 3V each and SHOULD (in theory) take a normal balanced charge.

I stopped the NiMH charge, reconnected the Balance Lead and started a LifePO charge. Thankfully, the charger accepted the command and my battery is now back to normal. PHEW!!!

UPDATE : AUG 2022

My 13.2V LifePO batteries are now heading toward their 4th birthday(!) and they’re still working perfectly. So dependable out in the field.

If you benefited from this post in any way or have something to contribute to the Blog, please comment below or drop  an email to m7mcqio83ro@gmail.com

73, Tom.