UPS - Replacing lead-acid with LifePo4

[Azurisz]

Hello folks! Question for you good people, since I think I know the answer but wanted to get a second opinion (or three). For an off-the-shelf consumer UPS like an APC UPS that has a single 12VDC 7AH lead-acid battery, are the lithium iron-phosphate batteries of similar size and form-factor drop-in safe for replacement? It looks like you can purchase very similar form-factor batteries from Li-Time and similar companies that claim to be compatible with lead-acid, but I don't see any documentation anywhere that definitively agrees or disagrees with that. Along those lines, since your basic consumer UPS does /not/ have the ability to set the battery chemistry (it assumes lead-acid), would the BMS in a LifePo4 battery correctly interface with them?

 

[millsan1]

Hello folks! Question for you good people, since I think I know the answer but wanted to get a second opinion (or three). For an off-the-shelf consumer UPS like an APC UPS that has a single 12VDC 7AH lead-acid battery, are the lithium iron-phosphate batteries of similar size and form-factor drop-in safe for replacement? It looks like you can purchase very similar form-factor batteries from Li-Time and similar companies that claim to be compatible with lead-acid, but I don't see any documentation anywhere that definitively agrees or disagrees with that. Along those lines, since your basic consumer UPS does /not/ have the ability to set the battery chemistry (it assumes lead-acid), would the BMS in a LifePo4 battery correctly interface with them?

I'd think there would be several issues.

The voltage for a given nominal is less in lead acid that lithium, so the lithium would never get to full charge.

The flat curve of lithium discharge would probably cause an issue with how the UPS reported % remaining.


That being said, I'd bet it would function.

 

[Azurisz]

I'd think there would be several issues.

The voltage for a given nominal is less in lead acid that lithium, so the lithium would never get to full charge.

The flat curve of lithium discharge would probably cause an issue with how the UPS reported % remaining.


That being said, I'd bet it would function.

Yep yep, I kind of figured that was the case but was curious if anybody else had experience with this application. I'm not too concerned about the runtime since its not expensive to vastly over-size the lithium battery. Mostly my only concern here is safety and reliability, with safety being #1 above all. Just hate the idea of using lead-acid or AGM when lithium is still coming down in price further and is going to easily last 4-5x the calendar life.

 

[DIYrich]

Big problem is the UPS may not be designed to run more than 15 minutes at a time.

 

[bolhuijo]

The main issue I see is that UPSs often flog these little batteries like rented mules. My Cyberpower 1500VA UPS uses a pair of these small form factor batteries that are very commonly used. 1500VA at 24V is 62.5 Amps. For a 7Ah battery that's a 9C discharge rate. The cute little LiTime 6Ah battery with that same physical form factor can do 30 Amps for 5 seconds. I have one for some solar lights and it's great but it would not survive in the UPS.