APC BX1350M battery teardown
Also Sold As / Retail Channel Equivalent: BX1350M-LM60 Same OEM manual or cartridge listing.
- Bare cells needed
- 2 x 12 V 7 Ah
- Max DC draw
- 41.2 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
- 1350 VA / 810 W
- Topology
- Line Interactive
- Waveform
- Simulated / Stepped
- Transfer time
- 8ms typical : 10 ms maximum
- OEM list price
- not published
- DC bus
- 24 V
- Last verified
- 2026-11-01
- LiFePO4 at full load
- RED
What battery does the BX1350M actually use?
The BX1350M 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 | 1350 VA / 810 W | T1 se.com |
| Topology | Line Interactive | T1 se.com |
| Waveform, in the OEM's words | Stepped approximation to a sinewave | T1 se.com |
| Transfer time | 8ms typical : 10 ms 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 BX1350M pull?
At its full 810 W rating, the BX1350M pulls about 41.2 A from its 24 V bus, and about 47.0 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 |
| 300 W | 15.2 A | 17.4 A |
| 405 W | 20.6 A | 23.5 A |
| 810 W | 41.2 A | 47.0 A |
Is LiFePO4 safe in the BX1350M?
A 12 A BMS limits the BX1350M to about 236 W, well below its 810 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
BX1350M: 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 810 W |
|---|---|---|
| 10 A | 197 W | 24% |
| 12 A | 236 W | 29% |
| 15 A | 295 W | 36% |
| 20 A | 394 W | 49% |
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 BX1350M run on each battery?
APC publishes about 10.1 min at 405 W and 2.5 min at 810 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 | 4.5 hr | 6.4 hr | 4.3 hr |
| 60 W | 1.6 hr | 2.4 hr | 2.4 hr |
| 100 W | 52 min | 82 min | 1.6 hr |
| 200 W | 23 min | 38 min | 53 min |
| 300 W | 14 min | 24 min | 0 min, BMS trip |
| 405 W | 10 min | 17 min | 0 min, BMS trip |
| 810 W | 2.5 min | 4.4 min | 0 min, BMS trip |
| Load | APC published | Raw Peukert | This site | Source |
|---|---|---|---|---|
| 405 W | 10.1 min | 9.8 min | 10.1 min | T1 se.com |
| 810 W | 2.5 min | 4.3 min | 2.5 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 BX1350M?
There are three routes for the BX1350M. 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 | 810 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 | 1000 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 8ms typical : 10 ms maximum, so check that your PC tolerates it.
How do you move the BX1350M 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 BX1350M alarms and fault codes mean?
APC Back-UPS Pro BX user guide lists 13 signals we track for the BX1350M. Only 2 of them point to the battery, and 8 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.
| Signal | Meaning | What to do | Battery swap? | Source |
|---|---|---|---|---|
| 4 beeps every 30 seconds | Running on battery. Usually a power cut, not a dead battery | Save your work. This alone is no reason to replace the battery. | Not a fault | T1 manual |
| Continuous tone | The battery backup outlets are overloaded | Unplug something. A new battery won't help. | Do not buy batteries | T1 manual |
| Chirps every 2 seconds | Battery disconnected | Reseat the battery connector before you order anything. | Check first, then decide | T1 manual |
| Continuous chirping | The battery failed the automatic test | Replace the battery. Mute pauses the chirping. | Path A swap fixes this | T1 manual |
| Replace Battery icon | End of battery life | Replace the battery as early as you can. | Path A swap fixes this | T1 manual |
| F01 | On-battery overload | Turn it off, unplug non-essential equipment, turn it back on. | Do not buy batteries | T1 manual |
| F02 | On-battery output short | Turn it off, unplug everything, turn it on, then reconnect one item at a time. If it trips with nothing connected, contact support before buying cells. | Check first, then decide | T1 manual |
| F03 | On-battery Xcap overload | The manual says you can't correct this yourself. Contact support, and if the unit is out of warranty compare Path C. | Do not buy batteries | T1 manual |
| F04 | Clamp short | The manual says you can't correct this yourself. Contact support, and if the unit is out of warranty compare Path C. | Do not buy batteries | T1 manual |
| F05 | Charge error | The manual says you can't correct this yourself. Contact support, and if the unit is out of warranty compare Path C. | Do not buy batteries | T1 manual |
| F06 | Relay welding | The manual says you can't correct this yourself. Contact support, and if the unit is out of warranty compare Path C. | Do not buy batteries | T1 manual |
| F07 | Temperature | The manual says you can't correct this yourself. Contact support, and if the unit is out of warranty compare Path C. | Do not buy batteries | T1 manual |
| F09 | Internal error | The manual says you can't correct this yourself. Contact support, and if the unit is out of warranty compare Path C. | Do not buy batteries | T1 manual |
How do you reach the battery in the BX1350M?
On the BX1350M, the manual says: removable battery door. the manual names no tools. 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 | Removable battery door. The manual names no tools | T1 manual |
| Cell orientation | Not stated in the manual we captured | same manual |
| Harness connector type | Not stated in the manual we captured | same manual |
| Cell layout | 2 x 12 V, in series | inferred |