Continuous LiFePO charging?


Oct 30, 2019
I've gotten a bunch of conflicting information so I thought I'd bring the question here to be considered by more informed minds. I have a 100ah LiFePO in my RV along with a 5 amp LiFePO charger (pic/link below). I plan to stay hooked to shore power for a month or two this winter. Can this charger stay hooked up continuously to the 100ah battery without issues? Everything I can see says there should be no problem as the charger is intelligent and self regulating. I've heard from others that say you can't do this with a LiFePO.



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Generally speaking you do no leave Lithium based batteries connected to chargers after they are fully charged. Unless they are smart enough, of course.
The one pictured I'm not aware of, the name is not familiar to me. Being that it is in a brick form, it is possible that this unit is just smart enough to stop charging once voltage reaches a certain level and then wait until voltage drops below a certain level before resuming.
For instance, it could charge up to 12.8V, and then wait for the battery to drop to 12V before starting back up. Most lead acid chargers don't do this and will start back up around 12.6V, aka float charging. Float charging is not good on Lithium based batteries.
According to the specs on Amazon, it does charge correctly, with the correct CC/CV charge options.

However, I would probably look at a different device other than the one posted.

Safety concerns because the fuse is only for show. Lowered to one stars due to seller responce.
I just used this for the first time yesterday. It charged my battery just fine but I am a retired electronics engineer so I was testing it's safe operation. I pulled the fuse and no change. Others have written about the fuse holder not being connected and now I believe it is truly just for show.

There is no fuse!
I just finished charging a 100ah LiFePO4 battery with this charger. It charged the battery and when the fan kicked off I seen that the LED changed to green, so I disconnected it. While I was giving the battery time to settle so that I could check the voltage with my meter I was reading through the comments here and noticed several reports about the fuse not being connected to anything. So I opened mine up and looked inside to see the same scene I seen in other reviews on here.

Always check the reviews on a product and what the low star reviews are more importantly.
For the brick itself, it might be helpful to somehow attach at least a big ol heatsink to the black case, if it's going to be run continuously.
The 100ah battery is also Expert Power. They are known in the aftermarket laptop battery market and I have bought 15-20 of their batteries for laptops in the past and had been relatively pleased.

@harrisonpatm - The brick is fan cooled but you also made me think if I want to listen to that all the time and I'm sure it is a really cheap tiny fan and makes me wonder how long it will last in continuous operation? Hmm...

The batteries usually charge on a Renogy solar charging system but I can't rely on that during the winter months.
TBH, it wouldn't be hard to add some smarts to it so that it only comes on under certain conditions. For instance, you could add a timer that would allow it to come on at certain times during the day. Or use a smart switch that could be controlled with conditional formatting (would need something like home assistant or maybe even GoogleHome or Alexa or something) so that it comes on only when battery voltage drops below a certain level.
I was expecting the charger to do that in itself.
The biggest thing here is *when* it comes back on. For example, let's use a 1s battery voltage range.

Fully charged is 3.6V, and during discharge, you do not want the charger to kick back on when the cell hits 3.5V, even 3.4V might be too high still. This is considered "Floating" and could actually damage the cell chemistry drastically reducing its lifespan.

So in a 4s configuration, this would 14.0V for full, and 13.6V. This is waaay too close. Basically the charger would be hammering the battery constantly as lithium chemistry voltages can bounce pretty quickly. It's not unnatural for a lithium cell to drop 1-2% after "fully charged" as it settles. And then it levels out and won't drop any further. Lead acid doesn't do this quite the same and actually "needs" the over charging (aka charging to 14.5-15V for a "12V" system (which is actually 13.5V)). Lithium based batteries can't handle that

So you would need to make absolutely sure that the charger you keep connected won't hammer the battery just because it dropped 1-2% charge voltage.
A "real" LiFePO4 charger actually would monitor the input and output flow so that it only kicked on when charge "capacity" dropped by a certain percentage, not the voltage. LiFePO4 does not have a linear discharge curve like LiMN or LiCO (the other lithium cells usually 18650's etc).

So a constantly connected charger might only kick on/off based on voltage only and this would inevitably kill the cells sooner
...and the voltage would always be a moving target based on the inverter, fridge, fans, radio, etc. coming on and off. I'm thinking it would be triggered to charge quite frequently but top off at it's 14.4 volts max and shut off quickly. How well a LiFePO4 takes that kind of treatment I don't know.
These are LiFePO4's, so the voltage won't change a whole lot. That is why using a voltage dependent charger is not recommended. A LiFePO4 could go discharge at 10A for 30 mins and barely even drop in voltage. Even the most robust 18650 (non-LiFePO4 variants) would drop a few 10's of a volt during discharge.
This is why using a voltage based charger on them is a bad idea. It would either kick on/off way too often (meaning voltage trigger is only 0.1V or less from full voltage) or it would go for a long time and not start charging until the battery is about half used (trigger around 0.3V from full charge voltage). ((these numbers are based on 1s1p assumptions))

That's why i was saying you'd want a smarter charger that could detect wattage, or coulombs, going in/out of the battery and charge accordingly. They are a little more expensive, but they are far more reliable and won't beat your battery to bits electrically.

You can't just toss a dumb charger on a LiFePO4 and leave it and expect it to keep the battery in good condition for very long (and never leave one unattended on LiFePO4's or any lithium based battery, for that matter). The only good ones, and reliable ones, are the smart ones that do true monitoring of the battery.

Otherwise, you could end up with a destroyed battery after a year of abuse and have to replace it. Batteries aren't cheap, even if you can source the individual cells at low cost, it still costs time/money to replace.
There's two cases here, charging "in-use" cells & maintaining cells in "storage" & these scenarios are different.
In-use I'd fully charge, use, recharge, etc (see below re <0C temps).
For storage I'd use the cells down to approx 60-70% & leave there, charge a little if needed, they should hold charge for months no problem unless there's drain, eg the BMS or use, etc. Storage at full charge (ie over approx 80-90% SoC) is not considered ideal.
I'd also consider the temperature curve of the cells you have, ideal voltages may change if cells cold vs warm, etc.
Personally I don't like my cells going over about 3.40V at full charge at the typically about 15 to 30C temps here.
Regularly taking LiFePo4 cells to >3.50 damages them & doesn't give you more SoC, there's very little % above 3.40V
Balance in my packs becomes unstable if cells >3.40V, some cells start to rise fast.
In winter if the cells are below freezing you need to be very careful not to charge Li cells much or at all.
If they are above 0C charge gently & above about 5C normal charging should be OK but check the manufacturers spec for your cells.
charging "in-use" cells & maintaining cells in "storage"

This would be an "in use" scenario living in the RV (escaping northern winter) plugged into shore power with day to day activities (fridge/fans/pump/lights/etc.) in a climate well above freezing. I've gotten ridiculous comments in other places ("you can't use a 5 amp charger with a 100 ah battery" and of course you can it just takes longer to charge and I have charged the 100 ah battery when dead and it took a full day as expected). The charger is built for LiFePO4 and it is the charger sold by the battery maker. It turns off (? - turns the indicator light to green) and shows charged at 14.4 volts. The idea is that I can pull heavily off the 100 ah battery when needed and the little charger just puts it back slowly when I'm not using power. My worry is that it will frequently be hitting that 14.4 volt limit several/many times a day. But, how is this any different than the Renogy solar charge controller that handles charging in the summer?
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Yeah nothing wrong with a 5A charger there, sure slower but not a problem. Gentle charging is actually better for Li batteries.
14.4V is too high IMHO, as mentioned that's 3.6V/cell (4 cells in a "12V" LiFePo4 pack).
You could get cell swelling.
Maybe buy a suitable heavy duty diode & put in series with charger. That'll drop about 0.7V which would end up giving the cell about 3.425V, much better. Diode will get pretty warm but that's OK.
I second Redpacket: 14.4V is alredy quite high for LiFePO, this means 3.6V/cell and at a low charge current this means already significant stress for the cells. 3.4 or 3.45 V is already 100% SoC and any more doesn't do any good.
So i would look for a flexible power supply to adjust the voltage to your needs and set the voltage to 13.2 ... 13.6V for a constant trickle charge. This would be much safer for the batteries lifespan!;)

As a word-around you could use the suggestion of Redpacket with a diode (or 2 of them) in series. The voltage drop gets less when the current drops - so i would even use 2 in series.