APC SMT750RM2UC battery teardown
Also Sold As / Retail Channel Equivalent: SMT750RM2UCNC Same OEM manual or cartridge listing.
- Bare cells needed
- 2 x 12 V 7 Ah
- Max DC draw
- 25.4 A
- OEM cartridge
- APCRBC123
- Cell size
- 151 x 65 x 94 mm
- In inches
- 5.94 x 2.56 x 3.70 in
- Terminal
- F2 check yours
- Rating
- 750 VA / 500 W
- Topology
- Line Interactive
- Waveform
- Pure Sine Wave
- Transfer time
- 6ms typical : 10ms maximum
- OEM list price
- not published
- DC bus
- 24 V
- Last verified
- 2026-11-01
- LiFePO4 at full load
- RED
What battery does the SMT750RM2UC actually use?
The SMT750RM2UC uses APCRBC123, which holds two 12 V blocks in series rated 7 Ah on a 24 V DC bus. Each block fits a 151 x 65 mm bay with F2 terminals. This model has no serial-number split that we could find.
| Spec | Value | Source |
|---|---|---|
| VA and watts | 750 VA / 500 W | T1 se.com |
| Topology | Line Interactive | T1 se.com |
| Waveform, in the OEM's words | Sine wave | T1 se.com |
| Transfer time | 6ms typical : 10ms maximum | T1 se.com |
| OEM cartridge | APCRBC123 | T1 se.com |
APC lists a 24V 7Ah module, which is two 12V 7Ah blocks in series in the standard 151 x 65 mm format. We have no teardown, so check when you open it. APC lists this for the BR1000G, BX1350M and SMT750RM2UC. The two-cell layout is inferred from its 24V 7Ah rating. Full APCRBC123 teardown
How many DC amps does the SMT750RM2UC pull?
At its full 500 W rating, the SMT750RM2UC pulls about 25.4 A from its 24 V bus, and about 29.0 A as the battery sags to 21 V cutoff. Those figures assume 82% inverter efficiency, because APC doesn't publish one for battery mode.
| AC load | Nominal | At cutoff |
|---|---|---|
| 25 W | 1.3 A | 1.5 A |
| 60 W | 3.0 A | 3.5 A |
| 100 W | 5.1 A | 5.8 A |
| 200 W | 10.2 A | 11.6 A |
| 250 W | 12.7 A | 14.5 A |
| 300 W | 15.2 A | 17.4 A |
| 500 W | 25.4 A | 29.0 A |
Is LiFePO4 safe in the SMT750RM2UC?
A 12 A BMS limits the SMT750RM2UC to about 236 W, well below its 500 W rating. At full load the verdict is RED. Packs in series can drift apart on the charger, so balance them first. APC doesn't support this swap. Drag the slider below to test your own load.
RED: BMS trip hazard
- DC draw now
- 12.7 A
- At 21 V cutoff
- 14.5 A
- Safe AC load
- 236 W
SMT750RM2UC: lead-acid anchored to OEM half and full-load runtimes, LiFePO4 on a flat energy curve with inverter tare, at 82% inverter efficiency. A real inrush can trip a BMS below this ceiling. APCRBC123 teardown.
| BMS continuous | Safe AC load | Share of 500 W |
|---|---|---|
| 10 A | 197 W | 39% |
| 12 A | 236 W | 47% |
| 15 A | 295 W | 59% |
| 20 A | 394 W | 79% |
Balance every pack first. Two independent BMS boards on one series charger can drift apart, and one can cut off early. Series drift and 0 V lockout explained.
How long will the SMT750RM2UC run on each battery?
APC publishes about 16.1 min at 250 W and 5.5 min at 500 W on the stock cells, and our curve passes through both points. The 12V 9 Ah high-rate AGM option adds runtime in the same case. Drag the slider for your own load.
| AC load | Stock 7 Ah | 12V 9 Ah high-rate AGM | LiFePO4 10 Ah |
|---|---|---|---|
| 25 W | 4.1 hr | 5.8 hr | 4.3 hr |
| 60 W | 87 min | 2.2 hr | 2.4 hr |
| 100 W | 47 min | 74 min | 1.6 hr |
| 200 W | 21 min | 34 min | 52 min |
| 250 W | 16 min | 26 min | 0 min, BMS trip |
| 300 W | 12 min | 20 min | 0 min, BMS trip |
| 500 W | 5.4 min | 9.3 min | 0 min, BMS trip |
| Load | APC published | Raw Peukert | This site | Source |
|---|---|---|---|---|
| 250 W | 16.1 min | 17 min | 16.1 min | T1 se.com |
| 500 W | 5.5 min | 7.6 min | 5.5 min | T1 se.com |
Same footprint, 28.6% more rated capacity. Upgraded AGM scales from the anchored curve, with k = 1.18 standard and 1.12 high-rate. LiFePO4 uses a flat energy curve with inverter tare. Method.
Which replacement should you buy for the SMT750RM2UC?
There are three routes for the SMT750RM2UC. Path A swaps in two bare cells and reuses your harness. Path B adds LiFePO4 for loads under 394 W, by the listing's 20 A claim. Path C replaces the whole UPS, which makes most sense for units over six years old.
| Path | Best for | Load limit | Main risk |
|---|---|---|---|
| A: bare SLA swap | Lowest cost, any load | 500 W | Terminal or case mismatch |
| B: drop-in LiFePO4 | Light loads, long life | 394 W on the listed 20 A | BMS trip, charger mismatch |
| C: native LiFePO4 UPS | A unit over 6 years old, or high loads | 800 W | Slower transfer than this UPS |
Path A: the bare-cell SLA swap
Surge-safe, because AGM has no BMS to trip. 7 Ah and 9 Ah cells share the 151 x 65 x 94 mm case, so 9 Ah adds 28.6% rated capacity.
Path B: drop-in LiFePO4
Safe to about 394 W if the listing's 20 A BMS is continuous, or 236 W at 12 A. Check your load before you click.
Path C: a native LiFePO4 UPS
Worth it if this UPS is 6 or more years old, if a fault above isn't a battery problem, or if you need more than the BMS limit. Listings and reviews put Goldenmate's transfer at 8 to 20 ms, against this unit's 6ms typical : 10ms maximum, so check that your PC tolerates it.
How do you move the SMT750RM2UC harness to bare cells?
You move the factory jumper and leads from the old blocks to the new ones, in the same polarity. Unplug the UPS first, and tape each lead as it comes off, because the battery stays live. Sealed sleds must be opened first. No soldering is needed.
- Shut down the load, turn the UPS off and unplug it from the wall.
- Take a photo of the wiring. Open the battery door or sled and slide the pack out.
- Pull the red clip off the positive tab, and tape it straight away.
- Remove the black lead and tape it. Then lift off the jumper between the cells, with its fuse if your harness has one.
- Check the new cells have the right size and tabs, then add any adapters from the parts list.
- Fit the jumper first, from the positive of one cell to the negative of the other. Fit the leads one at a time, matching your photo, and remove the tape only from the lead you are fitting.
- Measure about 25 to 27 V across the two outer leads before you close the pack. Slide it back, plug in and charge for the time the manual gives before relying on it.
- Recycle the old cells at a battery retailer. Never bin lead-acid.
Sixty seconds is the best case for a loose-cell unit. Sealed sleds need opening first, and opening them may affect your warranty and APC's equipment guarantee.
How much do you save over the APCRBC123?
We can't state a saving for APCRBC123, because we found no published list price for it. Any figure here would be a guess, so this page leaves it out rather than estimating one for you. Compare the list price with your own quote.
| Item | Status |
|---|---|
| APCRBC123 list price | not published |
| Verified bare-cell reference | none |
What do the SMT750RM2UC alarms and fault codes mean?
APC Smart-UPS SMT user guide lists 4 signals we track for the SMT750RM2UC. Only 1 of them point to the battery, and 1 mean you should not buy batteries yet. Read your signal below first, because a new battery won't fix a charger, a relay or an overload.
The manual lists no separate Battery Disconnected or AVR Boost/Trim alarm in the text we captured.
| Signal | Meaning | What to do | Battery swap? | Source |
|---|---|---|---|---|
| Replace Battery icon on, beeps one minute every five hours | Weak charge | Recharge for at least four hours and self-test. Replace only if it persists. | Check first, then decide | T1 manual |
| Replace Battery icon flashing, one beep every 2 seconds | Battery not properly connected | Reseat the battery connector. | Check first, then decide | T1 manual |
| Replace Battery LED red | The battery failed its self test | Replace the battery. | Path A swap fixes this | T1 manual |
| Error LED on, constant beeping | Internal error | APC says not to use the UPS, and to have it serviced at once. | Do not buy batteries | T1 manual |
How do you reach the battery in the SMT750RM2UC?
On the SMT750RM2UC, the manual says: front bezel comes off first. rack unit. Inside there are two batteries of about 151 x 65 mm. Check the details below before you start, turn the unit off and unplug it first, and photograph the wiring so you can match it later.
| Field | Value | Source |
|---|---|---|
| Battery door access | Front bezel comes off first. Rack unit | T1 manual |
| Cell orientation | Not stated in the manual we captured | same manual |
| Harness connector type | Internal battery connector (per the manual) | same manual |
| Cell layout | 2 x 12 V, in series | inferred |