12 volt, 9ah LiFePO4 battery for under $40 delivered

[papaof2]

batteryhookup.com/products/12-8v-9ah-115-2wh-4s3p-lifepo4-battery

A nicely packaged 12 volt, 9AH LiFePO4 battery from Fuji Film $18 plus shipping ($12.18 for one, $12.55 for two to Georgia) + tax.

cell specs:
Nominal voltage: 3.2
Fully Charged Voltage: 3.65
Fully Discharged Voltage: 2.5
Recommended Max Continuous Discharge: 20a
Recommended Max Continuous Charge: 6a

Under $40 is a ball park price for a 12volt, 7AH AGM battery delivered. This probably not a standard size (no dimensions listed) and it has screw terminals on the long side of the battery but you need to consider the capacity. The battery is 4s3p, so the 20A per cell discharge becomes 60A from the battery. 60A at 12volts is 720 watts, so this should work with a lot of small to medium UPS units. It does need a BMS but you should be able to find one for a reasonable price, such as: two for $7.71 + $3.99 ship from Amazon
www.amazon.com/Acxico-Balance-Protection-LiFePo4-Battery/dp/B09GKGZ31B

Remember that an LiFePO4 battery with a BMS can't be damaged by being run to zero volts by a UPS - the BMS will disconnect the battery at a safe voltage and it can be charged several thousand times - consider these "lifetime" batteries for your UPS.

Deals like this usually don't last long, so go looking with credit card in hand if you're interested ;-)

===

I ordered two batteries. With shipping and tax the total is $49.55. The two BMS's from Amazon are $12 so each battery with BMS is $31 delivered - that is ball park for a 12 volt UPS battery. I have three ideas for these batteries:
1. use both as replacements for the two 12 volt, 7AH AGM's in the pure sine wave UPS.

2. individual replacements in some under 500 watt UPS units.

3. prime power for some more solar-charged lighting - a 20 watt panel might be adequate for lighting that's only used during power outages.

[papaof2]

If you look at the internal pix on the battery's page batteryhookup.com/products/12-8v-9ah-115-2wh-4s3p-lifepo4-battery you'll see some serious interconnecting strips - with 6 welds where each strip connects to a battery - pretty sure they are designed for 60 amp loads.

[papaof2]

My email from FedEx says I'll have the batteries tomorrow. Then I get to figure out which of several options will put them to work.
I may also try running the 2000 watt pure sine wave inverter off one battery with a 440 watt load on the inverter ("500 watt" work light). That's about 41-42 amps input to the inverter and I'll know whether the cells really can deliver the rated 20 amps per cell and perhaps 60 amps for the 4s3p configuration - at least for a couple of minutes ;-)

[papaof2]

Yesterday's email made the delivery date Saturday and the batteries are here. I have taken out the 7 security screws to be able to take the top off the case and actually measure the voltage (there's a marginally marked connector with small gold contacts but I would NOT trust it for more than 5 amps, maybe 10 amps in short term usage. I'll post some pix with measurements (inside and out) when I get that done. For a quick and dirty sizing, it's a little longer but otherwise about the same size as the typical 12 volt, 7AH AGM battery in many UPS units.

For now, the first battery is on charge with the PWM controller configured for charging the 12 volt LiFePO4 for the shed lighting because I have that source of the proper voltages for that charge - but using cords with alligator clips to connect to the ends of the battery string and bypass the built-in BMS which no one seems to know much about. When I pull the cells out of the housing, I'll check that BMS board for any recognizable chips.

The "wiring" is designed for high amps (or very low loss) as the width of the nickel connecting strip is about 2/3 the diameter of the cell. The BMS units I ordered from Amazon won't be here for 2 or 3 weeks so I'll not be doing major discharge or high rate charge until those arrive. Meanwhile, I can see how long it takes to charge each battery at a constant 2 amps (good indication of the AH capacity) and how they do on longer term low rate discharges. Does a discharge at a constant 0.45 amps (the 20hr rate) actually run for 20 hours?

From the manufacturer's markings, one battery was built in 2015 and the other in 2019. The low rate charge and discharge will also give me a picture of the actual capacity of each battery.

As I post this, they still have these batteries in stock: batteryhookup.com/products/12-8v-9ah-115-2wh-4s3p-lifepo4-battery

[papaof2]

I've been testing the smaller LiFePO4 batteries I got from batteryhookup.com. They are just a little bigger than a 12 volt, 7AH AGM battery (common size in UPS units) but the cells are rated at 3AH with a minimum of 2.85AH when new and 2.75AH after 1000 cycles. The cells are in a 4s3p configuration, so the battery is nominally 9AH. However, the cells are rated for 25 amps discharge each so the battery pack should be good for 70+ amps. I haven't done any loads that big yet but I did connect a 500 watt pure sine wave inverter (about 0.6A idle) and use it to power a 100 watt soldering gun. That 100 watts works out to about 9.2 amps at 12.8 volts, plus the 0.6 amp of the inverter's idle current, so the battery pack was providing 9.8 amps to heat that soldering gun and the voltage held at 12.8 volts for as long as I held the gun's trigger down. Pretty impressive for a battery that size ;-)

I do have a standard 4s LiFePO4 30amp BMS (the original BMS talks I2C, which I can talk to but it's not worth the time to figure out how to decode all the communications of that BMS's microprocessor when a generic replacement BMS is under $10. When the new BMS is in place and the battery has been on charge long enough for the cells to be balanced (probably multiple days since the battery has sat unused for a while), I'll try loading the battery to the limit of the BMS (30A * 12.8V = 384 watts * .85 for the efficiency of the inverter = 326 watts. I have a halogen stand lamp with a "300 watt" bulb and a dimmer, so I'll put a Kill-A-Watt in line and use the lamp's dimmer to bring the load up slowly and see how much load the battery can actually handle.

If nothing else, the two Fuji LiFePO4 batteries could be the basis of an "In the dark" powerbox, with 12 volt power, USB charging ports, some LED lighting and maybe some limited AC power. One battery (without its case) would fit in a small plastic "ammo" can I have, along with various 12 volt connectors (lighter socket, PowerPole, XT60, 5.5/2.1mm coax socket), a 12 volt to USB adapter and a small sine wave inverter (300 watts) mounted on the box or as the base of the box. Add a small solar charge controller and MC4 connectors and it would have solar charging capabilities. I have two 12 volt to laptop power adapters with an assortment of connectors for various brands of laptops - definitely the adapters for the Dell laptops.

I spent maybe 20 minutes standing up and disassembling the batteries enough to be able to read the manufacturer's info on the cells. They're made by Murata and the datasheet is available online. Also took pictures of the original BMS and the wiring of the balance leads. My back/leg pain has improved a little, because I was able to stand that long after medicating with the Rx pain med - my stand and work time has been much shorter. Yes, I'm improving but it's like watching oil-based paint dry on a cold, rainy day :-(

The Murata datasheet and the label on the cells both say "Li-Ion" but the cell's resting voltage and its charge and discharge voltage limits make it LiFePO4.

Yet another project that I am making very slow progress on...

[papaof2]

The other consideration for a BMS is that the original I2C BMS does NOT connect the battery to its output terminals until the BMS gets the correct command from the computer that monitors and controls the large number of battery packs that make up the power unit for Fuji device that uses these battery packs. Easier/cheaper for me to replace the BMS's than to build a control device for two battery packs. If I had 200 of those packs, building my own controller would be reasonable and sacrificing one I2C BMS to determine how it works would be the cost of doing business ;-)

The original price of these battery packs? New: $3719, plus shipping. Used, tested on eBay: $305. I'd say there's some serious electronics on that BMS board. I may explore those electronics IF the chips on the BMS board have trackable numbers but that's a future project to satisfy my curiosity. I want the packs functional so I can do some higher current testing now, so I'll see about replacing at least one BMS tomorrow. The 30 amp BMS will allow doing some serious testing without getting near the limits of the cells used to build the battery pack. For that, I'd need a 60 amp or bigger BMS.

[papaof2]

I've replaced the BMS in the Fuji battery pack and it's working - at least well enough to allow partial discharge and recharge. When the current charge finishes, I'll do a metered discharge until the BMS low voltage limit disconnects the battery and see what this battery's actual AH is. Then I get to spend the better part of two hours doing the same to the other battery tomorrow or maybe the next day. Not hard, just detailed - such as cutting the power tabs from the battery pack to fit the spacing of the B+ and B- tabs on the BMS and trying to get 3/8" wide nickel strip hot enough to melt solder...

I've been sleuthing the original BMS with a large lighted magnifier and the microprocessor chip is an Atmel MEGA16HVB which is designed for all types of battery protection for 2, 3 or 4 cells. I found an abbreviated copy of the datasheet (about 20 of the 200+ pages). Some of the details require that you sign a Non-Disclosure Agreement (NDA) to get a copy. Among other things, there are multiple levels of security available in the chip (to protect the code you've written). Not sure if I'm that curious, although it would be nice to know the I2C communications sequences for "turn on", "turn off" and to read the voltages of the various cells.

If I had a "cheat sheet" for that, I have a Bus Pirate board which can read and interpret all types of computer communications - but first you must get the chip you're curious about to start talking...

[papaof2]

Running the battery pack to BMS low voltage cutoff at 0.45 amp (0.05C - the "20 hour" rate) gets 7.49AH as the first battery pack's capacity. The other battery tested a little higher when discharged to a fixed voltage so it should test out above 8AH.

I did some testing of the new BMS, including an unintentional "short circuit" test when connecting a 500 watt pure sine wave inverter to the pack's XT60 power connector. The BMS recovered from the short after about 5 seconds so that feature does work. I then ran a halogen light with a dimmer up to 115 watts and ran it from the battery pack for a couple of minutes - that was about 11 amps, per the clamp-on ammeter. Like the small UPS units, it was drawing some serious power from the battery but the battery voltage held up nicely. It should, as the cells used are rated for 25 amps discharge and they are in a 3p configuration. If I had a 75 amp BMS, I could get 75 amps for 0.09 hour or a little over 5 minutes. This would make a nice jump start pack if the connecting strips were a little bigger and I had a big BMS for it ;-) On the other hand, I might be able use it as a replacement for the battery on the riding mower - $25 for a bigger BMS beats $65-$75 for a lead-acid battery with a max of 3-4 years life. I should check out the jump start capability as a basic 100 amp BMS is under $30...

Checking the battery after it was recharged, the cells were all the same voltage - to the nearest 0.01 volt - so the BMS balance circuit seems to be working - or the cells are top of the line cells. The original BMS did have "Med Grade" on the circuit board.
If these battery packs will fit in the 800 watt pure sine wave inverter, I have a good 24V, 40A BMS to use with them - need to give that more thought and I'm wishing I'd ordered several more of the batteries - they were only on the batteryhookup.com web page for a day or so...

[papaof2]

Yet another small backup test today. The Fuji battery pack is powering a 300 watt pure sine wave inverter which has a 100 watt incandescent bulb as the load. There's also a handed electronic clock plugged in as an accurate run time meter.

A quick check with the clamp-on DC ammeter shows a draw of 8.1 amps so the pack should reach low voltage cutoff in about 50-55 minutes. That's 9.0 volts. However, the inverter's tested low voltage shutdown is 9.4 volts so it should shut down with a "low battery" alarm (yes, the equipment I use is often tested to its rated operational limits).

Just another bit of knowing "How well does it work when...?"

I still haven't pulled the batteries in the 800 watt pure sine wave UPS to check for size...

[papaof2]

That pack ran the inverter with its 100 watt load for 54:40 so my estimate was good.

The other Fuji pack ran that load for 61:20 so it is "a little higher".

Now I'm testing the battery bank on the backup power system. I separated the batteries and tested each one separately yesterday. Now that they're charged, it's time to do the low current discharge of the AGM bank (0.01C discharge to 50% DOD: 12.3 volts)

That should be finished between 4AM and 8AM tomorrow - then a fast recharge with two MPPT charge controllers pumping something over 400 watts into the battery bank. Then another discharge but at 0.1C (around 42 amps) to see what the AH capacity is at the 10 hour discharge rate. I'm 80% sure I'll have to replace the battery bank this year but I'm ensuring I've done all the tests.

The LiFePO4 cells I'm looking at are listed as >4000 cycles which is 10.95 years at one charge / discharge cycle a day.
I think I might consider those "lifetime" batteries. :-)

[papaof2]

I finally got the Fuji/Murata (Fuji label outside but the battery is made up of Murata cells) LiFePO4 battery installed in the shed's solar lighting today (in place of the two AGM batteries that were ages 4 years and 4 1/2 years). In a quick test (2 minutes) the flicker in the lights was gone. I'll do a longer test after dark so I can be inside the house and watch the light in the shed's window in air conditioned comfort ;-)

Replacing those batteries with two 7AH AGM batteries would have been about $50 and those batteries would then have needed replacement in about 5 years. I have two of the LiFePO4 battery packs that will fit in the plastic "ammo can" that I'm using to mount most of the components for the solar part of the lighting. The two batteries cost me $49.55 including tax and shipping or $24.775 each. Another $3 for a BMS and a couple $ for connectors (to make the battery easier to replace in the future) so I have about $30 in a battery that should last at least 10 years and possibly much longer with no more loading than it will have. Even if you repeatedly turn the timer to 60 minutes, the low voltage disconnect in the charge controller will protect the battery from overdischarge and, if that fails, the BMS is the second layer of overdischarge protection. Repeatedly turning the timer to 60 minutes would get about 3 hours of light before the overdischarge protection kicked in so there would be lighting for do things that take longer, such as changing a sparkplug or air filter on lawn equipment or a generator. In 20 years, someone might be in that shed after dark and turn the switch only to say "I didn't know there was power out here." ;-)

However, I did due diligence testing in advance, using a load similar to the the lighting, a windup timer set to 20 minutes and a "solar" power input limited to just under 10 watts - realistic for a 30 watt panel on a partly cloudy day. The load was about 14 watts, so the "solar" input could not keep up with the load, just part of it (real world on a partly cloudy day and there will be no solar input after dark).

The tests included "daytime" use of the lights (solar managing half the load, the battery the other half) and "night" use of the lights (the battery handling all the load).

The recharge time was directly proportional to the discharge time. I might be able to charge this battery directly from the 30 watt solar panel, just using the BMS to handle the charge level and the low voltage shutdown but I prefer using the solar charge controller because I can adjust the optimum charge voltage (less than the BMS's overvoltage disconnect) and my preferred load disconnect voltage - and I can monitor the charge controller for the daily, monthly and yearly solar and battery use statistics. I'll set that monitor up tomorrow as the temperature and humidity are too high for me to work outside in the shed for more than maybe 10 minutes at a time. I hate being old!