Replace the UPS battery or the whole UPS? APC and CyberPower cartridge guide

A UPS that used to give you time to shut down now barely gives you time to swear. If it still handles your load, has no hardware fault and only needs a battery, keep it: buy the exact maker cartridge. Replace the whole UPS when you need more watts, a different output waveform or a fix for failing electronics.

Cartridge matches and procedures come from the makers; status fields come from NUT documentation, checked October 25, 2026.

Keeping the UPS and upgrading its monitoring? Our UPS network-card compatibility guide separates APC SmartSlot and CyberPower expansion cards from the USB/NUT route.

The quick answer: keep the good box

For an APC BR1500MS2, choose APCRBC163. For a BX1500M, choose APCRBC124. The SMC1500C tower takes RBC6. Those are three different cartridges, even though all three UPS names contain “1500”.

For the CyberPower CP1500PFCLCD, start with the serial label: CXX means RB1290X2; CR9, CXF or CQC means RB1280X2B. That one glance matters more than the front-panel styling.

Already outgrown the unit? Start with our UPS buying guide and rack sizing and graceful-shutdown guide. A fresh cartridge restores the battery side of the job; it leaves the UPS’s watt limit, outlets and waveform unchanged.

Is the battery actually done?

Start with the warning on the UPS, then put it in context. The APC BR1500MS2 manual lists three reasons for disappointing runtime: too much connected load, a recently discharged battery and a battery at the end of its useful life. Charge it according to the manual and compare runtime at the same load before blaming age.

A replace-battery warning that persists after the maker’s recharge and self-test procedure is the clear cartridge-shopping signal. The SMC manual says to recharge a weak battery for at least four hours, run a self-test and replace it if the problem persists. It also distinguishes a flashing replace-battery indicator caused by a poorly connected replacement pack.

CyberPower’s REPLACE icon likewise covers a disconnected or worn battery. Its E01/E02 charger faults go to CyberPower support, rather than straight into your shopping basket. Those fault meanings and the replacement steps are in the CP1500PFCLCD manual.

For age, APC gives a typical battery life of three to five years under normal use and recommends replacement within that period, no later than five years. That’s a battery-service interval, not a countdown to throwing away the chassis. Heat and frequent discharge also affect life, so keep the battery date with your maintenance notes.

Match your UPS to its cartridge

Read the full model on the rear label before ordering. SMC1500C tower and SMC1500-2UC rackmount are different models; APC’s manual assigns the latter APCRBC157 instead of RBC6.

UPS on your label	Maker replacement cartridge
APC BR1000MS	APCRBC160
APC BR1500MS2	APCRBC163
APC BX1500M	APCRBC124
APC SMC1500C tower	RBC6
CyberPower CP1500PFCLCD, serial starts CXX	RB1290X2
CyberPower CP1500PFCLCD, serial starts CR9, CXF or CQC	RB1280X2B
Eaton 5SC1000	744-A2278, quantity one
Eaton 5SC1500	744-A2279, quantity one

The APC Back-UPS rows come from its US/Canada replacement lookup; the SMC tower row comes from the operation manual. CyberPower publishes the serial split in its CP1500PFCLCD data sheet. If your CyberPower prefix falls outside those groups, ask the maker to identify the pack from the full model and serial.

The Eaton units also appear in our UPS shortlist, so their matches belong here: use Eaton’s exact 5SC1000 lookup or 5SC1500 lookup to order through its replacement route.

Which cartridge should you pick?

APCRBC163 is the BR1500MS2 pick, including when you bought that UPS for its sine-wave output and USB management. Keep those useful features and renew the battery.

APCRBC124 is the BX1500M pick when its existing output and capacity still suit your equipment. If the actual upgrade you want is pure sine wave, head back to the UPS guide: a cartridge swap leaves this model’s stepped output unchanged.

RBC6 is the SMC1500C tower pick. Match the tower model, not an almost-identical rackmount name. APC includes the battery installation and disposal instructions with its RBC.

RB1290X2 and RB1280X2B are two separate CyberPower picks, divided by the serial prefixes above. Buy the complete maker cartridge that the lookup names, rather than assembling a pack from loose cells and a familiar-looking connector.

Read the battery story in NUT

On a system already running Network UPS Tools, use its read-only upsc client. Substitute the UPS name configured in your NUT installation:

upsc UPSNAME

Look through the returned fields for:

• battery.charge — charge level, in percent.
• battery.runtime — the reported remaining runtime, in seconds. Compare readings at a similar load and charge level.
• battery.date — installation or last-change date; battery.mfr.date is the manufacturing date, a separate field.
• ups.test.result — the last self-test result.

Those meanings come from NUT’s standard variable list. Your driver exposes the fields your UPS supports; a missing runtime or date field means “not reported”, not zero. A full charge bar describes charge level, so read it alongside the test result and runtime trend.

upsc reads status; it doesn’t start a self-test or record a replacement date. Use the UPS controls or its management software for those jobs. Keep the graceful-shutdown setup working while you maintain the battery: a fresh pack and an orderly shutdown make a useful team.

Your 10-minute replacement checklist

Use this as a short hands-on work plan, with charging and the final test afterward. Have the exact cartridge and its installation sheet beside you before starting.

1. Save work and shut down the protected equipment. For the power-off route, switch off the UPS and unplug its AC input. CyberPower explicitly requires connected equipment and the CP1500PFCLCD to be off and unplugged for its battery procedure.
2. Clear the workspace. Remove rings, watches and other conductive jewellery, and use insulated-handled tools as CyberPower instructs. Keep loose metal away from battery terminals.
3. Open the battery access panel described in your model’s instructions. Follow that panel’s screw and connector sequence; leave the rest of the UPS enclosure alone. If a pack is swollen, leaking or stuck, stop and contact the maker for service.
4. Swap the specified cartridge. Follow its lead routing and polarity diagram, seat the connectors and reinstall the retaining hardware. CyberPower says to replace both batteries together; use the complete matched replacement pack.
5. Close the compartment, restore AC and start the UPS. Reconnect your equipment once the UPS is ready. Keep the old pack in the replacement packaging for recycling.
6. Record the installation date and confirm the replacement in the UPS UI where supported. Then allow the required charge and run the maker’s self-test.

Can you hot-swap instead?

APC’s Smart-UPS hot-swap guidance includes the SMC family: connected equipment can stay powered during a supported cartridge change. There is no battery backup while the pack is disconnected, so wait for stable utility power and follow the exact RBC instructions. The linked maker FAQ is in French; the SMC operation manual supplies the model-specific controls.

For the CyberPower here, use the shutdown-and-unplug procedure above. “User replaceable” and “hot-swappable” are different features.

Charge, acknowledge, test

CyberPower specifies 8–16 hours of recharge after replacement. That sits outside the short swap checklist. APC’s hot-swap guidance says to charge to 100%, then self-test.

On SMC models, APC’s replacement-status instructions say to hold MUTE + MENU for two seconds, use MENU to reach rb.0, then MUTE to select rb.1, confirming a new battery. Use the operation manual’s self-test controls afterward; its configuration menu uses St.1 to request a test.

Read the new status and check that the warning clears. If the UPS still reports a battery or charger fault after the specified charge and test, take that result to maker support instead of buying another cartridge on a guess.

When the whole UPS is the better upgrade

Keep the existing unit when its capacity, waveform, management and physical condition still suit your rack. Replace or service it when the problem is failing electronics, not just an exhausted battery.

A larger NAS, GPU box or extra switch may have outgrown the original watt rating. Rework the load in the UPS sizing guide, then choose a unit with the capacity and USB/NUT shutdown route you need. If pure sine wave is now part of your requirements, pick it at the UPS level.

Treat a lithium UPS as its own product family, with its own maker-approved replacement or service procedure. The APC and CyberPower lead-acid cartridge instructions here specify matching battery type and count; they aren’t a lithium-conversion recipe.

Finish the job: recycle the old pack

APC’s US RBC recycling program provides a prepaid return-label route for customers who buy a genuine APC RBC. Follow its packing and return instructions. CyberPower’s manual directs you to proper battery recycling and notes that many lead-acid battery retailers collect spent packs; arrange an accepting collection point before taking yours in.

Label the new battery’s installation date, keep the cartridge number with it, and leave the shutdown software enabled. Next time the UPS starts complaining, you’ll have its history ready—and a much shorter shopping list.