AC charge controller for lifePO4 battery?

[WRTC928]

I know very little about lifePO4 batteries except that they don't weigh much and they're popular with off-grid preppers who use solar chargers. I understand they're subject to overcharging which can damage the battery. The charger I see recommended most is a "hybrid inverter" charger which is an AC and solar charger with a built-in charge controller, but they're really expensive and I don't need the solar charging feature. I want to put a battery backup on my repeater and keep it charged from the house AC. I'd also like to have a battery I can grab and go if I think I may be using my vehicle radio a lot on a particular day to avoid running down the vehicle battery. Is there a charge controller for the PO4 that will keep it topped off similar to what the "float charger" does for a lead-acid battery? Something that I can just leave hooked up and plugged in without worrying about it? I've done a search for them, but I can't find one that specifically addresses this use case. 

[Lscott]

13 minutes ago, WRTC928 said:

I know very little about lifePO4 batteries except that they don't weigh much and they're popular with off-grid preppers who use solar chargers. I understand they're subject to overcharging which can damage the battery. The charger I see recommended most is a "hybrid inverter" charger which is an AC and solar charger with a built-in charge controller, but they're really expensive and I don't need the solar charging feature. I want to put a battery backup on my repeater and keep it charged from the house AC. I'd also like to have a battery I can grab and go if I think I may be using my vehicle radio a lot on a particular day to avoid running down the vehicle battery. Is there a charge controller for the PO4 that will keep it topped off similar to what the "float charger" does for a lead-acid battery? Something that I can just leave hooked up and plugged in without worrying about it? I've done a search for them, but I can't find one that specifically addresses this use case. 

You can look at some of these.

https://www.bioennopower.com/collections/battery-chargers

[tweiss3]

Yea, all my LiFePO4 batteries are bioenno, and I bought their charger with the battery. They do stop charging (LED goes green from red) when the battery is full.

[Seapup]

Battery Tender markets models that support your LiFePO4 use case. Here are a few of many:

 

https://www.amazon.com/gp/product/B06X9GGNZC/

https://www.amazon.com/Battery-Tender®-Lithium-Selectable-Charger/dp/B09XP77JCS/

 

[SteveShannon]

One week ago I attended a four hour course on safety and lithium batteries.  We saw some very alarming videos that highlighted how dangerous lithium batteries can be. It was chilling. One in particular showed a young man get into an elevator with the battery from a e-bike. It began smoking and flashed quickly into an inferno that killed him before the elevator doors re-opened. You’re right in wanting to incorporate a charger that protects the battery, but you should also consider where you place the battery so that if it fails it doesn’t destroy your house.

[Socalgmrs]

With how horrible lithium is for the environment both when mining and later and how dangerous they are I won’t have them any place near my home or cars.   Even at work we will not carry them in our trucks.  We work with 48v lithium and we let ups deal with that.  We have had many trucks and vans burn to the ground with lithium.  Especially bad while driving on The freeway. 
 

you can get some very nice, however heavy, agm battery’s for much less money.  One of my radios in the house runs off a 100amh agm and a trickle charger and in the truck I have a hard mounted 80amh agm mounted under the hood that is isolated from the truck batteries but charges off the alternator.   

[Lscott]

54 minutes ago, SteveShannon said:

One week ago I attended a four hour course on safety and lithium batteries.  We saw some very alarming videos that highlighted how dangerous lithium batteries can be. It was chilling. One in particular showed a young man get into an elevator with the battery from a e-bike. It began smoking and flashed quickly into an inferno that killed him before the elevator doors re-opened. You’re right in wanting to incorporate a charger that protects the battery, but you should also consider where you place the battery so that if it fails it doesn’t destroy your house.

How stable the battery is depends on the Lithium chemistry used. The worse are Lithium Ion types, followed by Lithium Polymer. The most stable is the Lithium Iron Phosphate type.

[UncleYoda]

38 minutes ago, Lscott said:

The worse are Lithium Ion types

And that's what all (that I've bought or looked at) the HTs use.  I haven't had any smoke or even get hot. (lucky?)  [When talking a lot using a battery eliminator that does get hot but it isn't a battery.]

[Lscott]

On 4/2/2025 at 12:24 PM, UncleYoda said:

And that's what all (that I've bought or looked at) the HTs use.  I haven't had any smoke or even get hot. (lucky?)  [When talking a lot using a battery eliminator that does get hot but it isn't a battery.]

All the Lithium battery packs I have, at least for Kenwood radios, have a protection circuit in them. I don't know if they protect against over charge, fairly sure they do, but they do work to prevent over discharge. When the terminal voltage drops to a bit under 6VDC the output voltage will suddenly drop to zero. I've run into this while testing my packs for usable remaining capacity with an electronic load. Also the radios seem to alarm out and shut down at the 6VDC mark too.

https://forums.mygmrs.com/gallery/image/248-2117323252_batterypacktestingjpg/?context=new

I found a while back a web site where a guy did a tear down of a K2 Energy 7Ah LiFePO4 battery pack. You can see the Chinese protection module inside.

 

K2 Energy K2B12V7EB LiFePO4 Internals.pdf

[UncleYoda]

Lithium ion batteries do drop quick near the low end.  But I don't see the connection to over-heating.

[Lscott]

11 minutes ago, UncleYoda said:

Lithium ion batteries do drop quick near the low end.  But I don't see the connection to over-heating.

The attached paper, from my personal electronic technical library, goes into some detail on the various failure conditions for Lithium cells. Worth the read.

Safety of lithium-ion batteries.pdf

[WRTC928]

5 hours ago, SteveShannon said:

One week ago I attended a four hour course on safety and lithium batteries.  We saw some very alarming videos that highlighted how dangerous lithium batteries can be. It was chilling. One in particular showed a young man get into an elevator with the battery from a e-bike. It began smoking and flashed quickly into an inferno that killed him before the elevator doors re-opened. You’re right in wanting to incorporate a charger that protects the battery, but you should also consider where you place the battery so that if it fails it doesn’t destroy your house.

That's good to know. I was not aware of that.

[WRYZ926]

Fire departments pretty much have to let electric vehicles burn themselves out because of the lithium batteries. Lithium is like white phosphorus in that it will keep burning when you try to put it out. 

I'm not super familiar with putting out lithium fires.  I do know the only way to stop white phosphorus from burning is to bury it so that there is no oxygen. And it will reignite if exposed to the open air.

Willy Pete grenades are fun to play with and the white phosphorus will burn straight through even some of the thickest armor plate. White phosphorus grenades are great for when you have to destroy equipment and vehicles.

[WRTC928]

21 hours ago, WRYZ926 said:

Willy Pete grenades are fun to play with and the white phosphorus will burn straight through even some of the thickest armor plate. White phosphorus grenades are great for when you have to destroy equipment and vehicles.

My father had burn scars on his chest from a bit of WP spray he got in the Korean War. I never thought to ask him if the grenade was Chinese or American. 

Speaking of destroying equipment, in 1978, US troops on the listening posts in Iran had to pull out in a hurry and leave their highly classified comm equipment behind. They applied something that looked like fruit roll-ups and lit it. In fairly short order, it reduced millions of dollars' worth of equipment to slag. I don't know what that stuff was, but I'll bet I could have some fun with it.

[WRTC928]

As I said, I don't know much about these batteries, and it gets confusing to read the info on the sales sites. They never say whether the thing will safely act like a trickle charger or not. 

[WRTC928]

And a follow up question... Is there any reason I can't hook two 50 Ah lifePO4 batteries in parallel to provide 100 Ah like you can with lead-acid batteries? I think some solar charging systems do something similar, but I'm not sure. I can't think of a reason why it would be a problem, but this is uncharted territory for me.

[SteveShannon]

2 minutes ago, WRTC928 said:

And a follow up question... Is there any reason I can't hook two 50 Ah lifePO4 batteries in parallel to provide 100 Ah like you can with lead-acid batteries? I think some solar charging systems do something similar, but I'm not sure. I can't think of a reason why it would be a problem, but this is uncharted territory for me.

Lead-acid batteries have measurable internal resistance that will limit the current flow between them. LiFePo batteries have very little internal resistance so connecting two batteries together that have different voltage levels could be exciting when the current between them spikes. I can only assume that some kind of balancing circuit would be necessary to parallel them. 

[WRYZ926]

You can safely connect LiPo4 batteries in series or parallel or both.  LiPo4 batteries do have a BMS (battery control module) that protects them. Always use the exact same size and capacity batteries when connecting multiple LiPo4 batteries together. It is also advisable to make sure they are the same age. IE you don't want to connect a brand new inline with an old battery

I run 4 10AH LiPo4 batteries hooked in parallel in my small battery box and two 50 AH LiPo4 batteries connected in parallel in my big go box. I also have an Apache case with two 10 AH LiPo4 batteries and a spot for my Xiegu G90. I can run those two batteries separately or in parallel if I want.

[tweiss3]

From Bioenno

 

Long story, you can but you probably shouldn't.

 

 

[WRYZ926]

Each manufacturer is going to have different instructions when it comes to using their batteries. I use Redodo brand batteries and they do not have any warnings on their website that I could fine.

How to Connect Batteries in Series and Parallel?

As always, consult the manual that comes with your batteries or consult the manufacturer directly.

Make sure that what ever charger you use is designed for lipo4 batteries. I use a Bioenno 5 amp charger for my 10 AH batteries and a Redodo 10 amp charger for the 50 ah batteries.

[LeoG]

7 hours ago, SteveShannon said:

Lead-acid batteries have measurable internal resistance that will limit the current flow between them. LiFePo batteries have very little internal resistance so connecting two batteries together that have different voltage levels could be exciting when the current between them spikes. I can only assume that some kind of balancing circuit would be necessary to parallel them. 

When you want to connect two or more LiFePO4 batteries together you top charge them individually and then when they are all fully charged you can put them in series or parallel.  If you put two batteries together that are of unsimilar charged state they might discharge into one another but the protection circuits in each battery will shut it down if the current levels get excessive and out of the set spec of the BMS.

[WRTC928]

19 hours ago, SteveShannon said:

Lead-acid batteries have measurable internal resistance that will limit the current flow between them. LiFePo batteries have very little internal resistance so connecting two batteries together that have different voltage levels could be exciting when the current between them spikes. I can only assume that some kind of balancing circuit would be necessary to parallel them. 

That's what I wanted to know. Thank you. Off-grid solar/battery arrays apparently typically have some sophisticated circuitry associated with them and it probably balances the voltages. 50 Ah will probably give me plenty of standby capability. Certainly enough to go swap the battery. I have damaged shoulders, and I prefer not to deal with the weight of a 100 Ah battery, especially if I want to take it somewhere else. I can always buy one later if I change my mind.

[WRYZ926]

I have a group 24 deep cycle lead acid battery along with a group 24 LiPo4 battery. The LiPo4 battery is half the weight of the deep cycle lead acid battery. The Lipo4 battery weighs 24 pounds while the lead acid weighs 48 pounds. I was using the lead acid battery to run the 45 ln thrust trolling motor on my 10ft Bass Pro Pond Hopper. I have switched to the group 24 LiPo4 batter for the weight saving. I still get the same performance and run time out of the trolling motor when using the LiPo4.

[WRTC928]

19 hours ago, SteveShannon said:

I can only assume that some kind of balancing circuit would be necessary to parallel them. 

Now that I know such a thing exists, it appears they're not prohibitively expensive. here and here $50 seems cheap enough to avoid blowing up my house.

[Lscott]

41 minutes ago, WRTC928 said:

50 Ah will probably give me plenty of standby capability

I have one of these 40Ah battery packs myself for emergency use. I also purchased the matching charger for it.

https://www.bioennopower.com/products/12v-40ah-lfp-battery-pvc-blf-1240a

The attached photo shows mine and the charger. The battery pack in the fanny pouch is a smaller LiFePO4 one and the matching charger to use when walking around.

Remember with a LiFePO4 battery you might not really need a 100Ah battery pack.

The typical Lead-Acid battery exhibits a "Peukert Effect", which is where the Lead Acid battery has lower usable capacity when discharged at high rates.

https://battlebornbatteries.com/peukert-effect/?srsltid=AfmBOoqoAjoBFTa9CHSm0C6i9hwZ_TdVi0DgazQTAiQ5bTzVMyMOrxyX

Further the voltage drops to 11.5 to 12 volts around 50 percent or so of remaining capacity. Most mobile radios are spec'd at 13.8 VDC +/- 15%, so the lower voltage limit is at 11.75 VDC. Look at the attached datasheet for a typical 12Ah sealed Lead Acid battery pack and check out the "Battery discharge characteristics" curves.

With a LiFePO4 battery, which doesn't suffer from the "Peukert Effect", you can use anywhere from 80 to 90 percent of the capacity and still be at 12.8 volts, well above the lower limit for portable mobile type radios. That means you can expect to get nearly the same usable operating time out of a LiFePO4 battery that you would expect to get out of a Lead Acid type with nearly double the capacity rating.

BP12-12.pdf

[WRTC928]

12 minutes ago, Lscott said:

I have one of these 40Ah battery packs myself for emergency use. I also purchased the matching charger for it.

https://www.bioennopower.com/products/12v-40ah-lfp-battery-pvc-blf-1240a

Remember with a LiFePO4 battery you might not really need a 100Ah battery pack.

The typical Lead-Acid battery exhibits a "Peukert Effect", which is where the Lead Acid battery has lower usable capacity when discharged at high rates.

https://battlebornbatteries.com/peukert-effect/?srsltid=AfmBOoqoAjoBFTa9CHSm0C6i9hwZ_TdVi0DgazQTAiQ5bTzVMyMOrxyX

Further the voltage drops to 11.5 to 12 volts around 50 percent or so of remaining capacity. Most mobile radios are spec'd at 13.8 VDC +/- 15%, so the lower voltage limit is at 11.75 VDC. Look at the attached datasheet for a typical 12Ah sealed Lead Acid battery pack and check out the "Battery discharge characteristics" curves.

With a LiFePO4 battery, which doesn't suffer from the "Peukert Effect", you can use anywhere from 80 to 90 percent of the capacity and still be at 12.8 volts, well above the lower limit for portable mobile type radios. That means you can expect to get nearly the same usable operating time out of a LiFePO4 battery that you would expect to get out of a Lead Acid type with nearly double the capacity rating.

BP12-12.pdf 333.57 kB · 0 downloads

Thanks. That's good to know.