On Wed, 4/2/2025 4:20 PM, Ant wrote:
Are those third party lithium battery replacements (e.g., https://a.co/d/bjBzSf4) safe and good to use for APC UPSes?
"The operating current of 12V 10Ah battery is 10A,
and the maximum instantaneous current is 30A(5 seconds)."
That means the battery can put out 120W continuously.
Now, work out the max power output of the APC = 650W
You're running a 650W UPS using a 120W (continuous) battery.
That does not sound right, somehow :-) And do you really want
to leave four or five additional batteries sitting on your
night table ? I think not.
The UPS will float charge them constantly at 13.5V .
Lithium do not float charge (officially, you're not
supposed to do that). Proper lithium charging requires the
charger to stop... and not start charging again, until the battery
is discharged somewhat. The APC does not know you have connected
LFP -- it is not a mind reader.
LFP (LiFeP04) chemistry is specifically selected for this product,
due to its "tolerance of abuse". NMC could not be abused
like this. You can put current into LFP, even when it
does not want the current. LFP has lower power density and the ability
to be abused on its charge cycle. It also has a slightly
higher charge cycle count than laptop batteries do (if you treat
them right). These cells are not used in laptops or inside phones
(not enough runtime, lower power density).
I don't really know, how to gauge when one of these is failing.
Sure, it might fail the once-a-day impedance test (which
lasts for a second or two), but how beat to death would
this particular battery chemistry be, when it triggers the
"beep" thing ? APC UPS only beep once on an impedance failure.
You can tell when an APC SPS (Standby Power Supply) UPS is
failing, by the metal case temperature. An ice-cold APC SPS
is working properly. If the APC gets lukewarm to the touch,
that means your lead acid pack has shorted-out cells inside.
Time to replace, when the housing gets even a bit warm.
The SPS type does not dissipate power when in quiet mode,
which is why it can be cold like that. When it floats the
battery at 13.5V, hardly any current flows into a "healthy" battery.
Maybe 5-10mA. How much current flows into the LFP pack ???
I don't know. And my livingroom seems a poor place for
pyrotechnical experiments.
*******
The price of a kilowatt hour of battery has dropped a lot over time.
This battery is priced as if the price had never dropped. It's still
a thousand bucks. You can put eight of these in parallel, but the advert
says the battery is limited to 50A discharge current (instead of the
100A by itself). With eight of those in parallel, you get 400A continuous.
You can put two of the batteries in series, making 24V @ 100A. But at that price, you won't be doing that. And because it has a pushbutton control,
you won't be buying that (it likely means a BMS test circuit is being
used as a power control). Batteries have cells, but they have a BMS
(Battery Management System) circuit board on top which monitors the
cells and may attempt to "balance" the battery during charging.
https://batterybrands.com.au/products/pylontech-rv12100-12-8v-100ah-1280wh-4s4p-lifepo4-battery-soc-indicator-m8-terminals-max-2s-or-8p-ip20-rating
At the price of those batteries, you don't abuse those with a float charge.
You would use a proper Lithium charger that cuts off the charger when
the pack is full. It would not fit into your APC, but it would be
a bit closer to the correct capacity numbers. And it's $1000 so you
won't be buying that anyway.
The State of Charge (SoC) indicator on that pack, is four LEDs and a push button.
You press the switch, and if four LEDs light up, the battery is full. Take
your finger off the test button and the LEDs stop illumination. Some laptop packs used to have a SoC like that on them. Four LEDs.
If I could find an authoritative source claiming "this was OK for X years",
I would tell you that. So far, I haven't seen a BatteryUniversity.com app note on this. That's our source of non-pyrotechnical battery operation info :-)
I believe some domestic Japanese UPS are using Lithium. I haven't checked lately, to see if anyone in North America has had the cheek to do that
(fire risk). No, you can't buy the Japanese one as it is the wrong voltage. That helps prevent grey-market sales of such. When they are good and
ready to make a 115V one, they'll make one.
Since they are constantly working on new battery designs, I believe one
day, we will be shed of the 3-year-drop-dead Lead Acid ones and we will
get a quality design. But it's not ready quite yet. Solid state electrolyte Li is one possible type. Expect abusive pricing on the batteries, as the
batteries will never match lead acid on price. People insist on selling
$100 per kWh batteries for $1000 per kWh. "Bad monkey bad".
Paul
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