The exact cells inside your UPS, what its alarm means, and whether LiFePO4 will trip

Your UPS is beeping and the OEM cartridge lists at up to $392. Here is what's inside it, what actually fits, and the math behind each answer.

The expensive UPS battery traps

Value	Trap	What goes wrong	See
$110	The plastic sled markup	APCRBC163 lists at $180. Two CSB 9 Ah blocks are $69.88 from a non-Amazon store, and you reuse the slide-on wire.	APCRBC163
51 mm	The BE600M1 width and terminal trap	A standard 65 mm battery jams in the slot, and the stock cell has asymmetric +F2/-F1 tabs.	BE600M1
236 W	The 1500 VA LiFePO4 blackout crash	A 12 A BMS trips above 236 W on a 24 V unit, while a CP1500PFCLCD can demand 50.8 A.	BMS limits
+28.6%	The CP1350PFCLCD serial split	CXY and CX5 serials take 9 Ah cells in the same case. CQB and CR8 use 90 mm cubes, and a 151 mm brick won't fit.	CP1350PFCLCD
6 V	The 1U rackmount battery trap	The OR700LCDRM1U uses two 6 V cells in a 35 mm tray. A 12 V battery won't fit and would double the pack voltage.	OR700LCDRM1U
E02	The charger code that isn't a battery	On CyberPower LCD units, E02 means the charger isn't charging. New batteries won't fix it.	CP1500PFCLCD

All 35 UPS models

Solver output for each model at its default hardware revision
UPS	VA / W	Waveform	Cartridge	Cells	Max DC	Safe at 12 A BMS	Serial split
BR1500MS2	1500 / 900	Pure Sine Wave	APCRBC163	2 x 9.4 Ah	45.7 A	236 W	No
BX1500M	1500 / 900	Simulated / Stepped	APCRBC124	2 x 9 Ah	45.7 A	236 W	No
BR1500G	1500 / 865	Simulated / Stepped	APCRBC124	2 x 9 Ah	44.0 A	236 W	No
BN1500M2	1500 / 900	Simulated / Stepped	APCRBC161	2 x 9 Ah	45.7 A	236 W	No
BE600M1	600 / 330	Simulated / Stepped	APCRBC154	1 x 6.5 Ah	33.5 A	118 W	No
BE850G2	850 / 450	Simulated / Stepped	RBC17	1 x 9 Ah	45.7 A	118 W	No
SMT1500C	1440 / 1000	Pure Sine Wave	RBC7	2 x 17 Ah	50.8 A	236 W	No
CP1500PFCLCD	1500 / 1000	Pure Sine Wave	RB1290X2	2 x 9 Ah	50.8 A	236 W	Yes
CP1500AVRLCD3	1500 / 900	Simulated / Stepped	RB1290X2E	2 x 9 Ah	45.7 A	236 W	No
CP1350PFCLCD	1350 / 880	Pure Sine Wave	RB1270X2C	2 x 7 Ah	44.7 A	236 W	Yes
CP1000PFCLCD	1000 / 600	Pure Sine Wave	RB1290	1 x 9 Ah	61.0 A	118 W	No
EC850LCD	850 / 510	Simulated / Stepped	RB1270B	1 x 7.2 Ah	51.8 A	118 W	No
BR1000MS	1000 / 600	Pure Sine Wave	APCRBC160	2 x 7 Ah	30.5 A	236 W	No
BX1000M	1000 / 600	Simulated / Stepped	APCRBC158	1 x 9 Ah	61.0 A	118 W	No
BE425M	425 / 255	Square Wave	Internal battery	Not replaceable	25.9 A	118 W	No
SMT1500RM2UC	1440 / 1000	Pure Sine Wave	APCRBC159	4 x 7 Ah	50.8 A	472 W	No
SMT2200C	2200 / 1980	Pure Sine Wave	RBC55	4 x 17 Ah	50.3 A	472 W	No
OR1500LCDRM2U	1500 / 900	Simulated / Stepped	RB1270X4	4 x 7 Ah	45.7 A	472 W	No
SMART1500LCD	1500 / 900	Simulated / Stepped	RBC1500	2 x 7 Ah	45.7 A	236 W	No
5S1500LCD	1500 / 900	Not verified	Eaton 5S cell pair	2 x 9 Ah	45.7 A	236 W	No
BR1350MS	1350 / 810	Pure Sine Wave	APCRBC161	2 x 9 Ah	41.2 A	236 W	No
BR1000G	1000 / 600	Simulated / Stepped	APCRBC123	2 x 7 Ah	30.5 A	236 W	No
BX1350M	1350 / 810	Simulated / Stepped	APCRBC123	2 x 7 Ah	41.2 A	236 W	No
BX850M	850 / 510	Simulated / Stepped	RBC17	1 x 9 Ah	51.8 A	118 W	No
BN1100M2	1100 / 600	Simulated / Stepped	APCRBC160	2 x 7 Ah	30.5 A	236 W	No
BE650G1	650 / 390	Simulated / Stepped	RBC17	1 x 9 Ah	39.6 A	118 W	No
CP1000AVRLCD	1000 / 600	Simulated / Stepped	RB1290	1 x 9 Ah	61.0 A	118 W	No
CP850PFCLCD	850 / 510	Pure Sine Wave	RB1290	1 x 9 Ah	51.8 A	118 W	Yes
LX1500GU	1500 / 900	Simulated / Stepped	RB1290X2	2 x 9 Ah	45.7 A	236 W	No
CST1500SUC	1500 / 900	Pure Sine Wave	RB1290X2	2 x 9 Ah	45.7 A	236 W	No
SMC1500-2UC	1440 / 900	Pure Sine Wave	APCRBC157	Not published	45.7 A	472 W	No
SMT750RM2UC	750 / 500	Pure Sine Wave	APCRBC123	2 x 7 Ah	25.4 A	236 W	No
OR700LCDRM1U	700 / 400	Simulated / Stepped	RB0690X2	2 x 8 Ah	40.7 A	118 W	No
CP1500PFCRM2U	1500 / 1000	Pure Sine Wave	RB1290X2D	2 x 9 Ah	50.8 A	236 W	No
5P1500R	1440 / 1100	Pure Sine Wave	EBP-0807	Not published	55.9 A	472 W	No

All 25 OEM cartridges

List price against a non-Amazon single-unit bare-cell reference
Cartridge	Inside	Bus	Terminal	List price	Saving
APCRBC163	2 x 9.4 Ah	24 V	F2	$180	~61%
APCRBC124	2 x 9 Ah	24 V	F2	$181	~61%
APCRBC161	2 x 9 Ah	24 V	F2	$164	~57%
APCRBC154	1 x 6.5 Ah	12 V	+F2/-F1	$101	~70%
RBC17	1 x 9 Ah	12 V	F2	$103	~66%
RBC7	2 x 17 Ah	24 V	NB	$392	~69%
RB1290X2	2 x 9 Ah	24 V	F2	$117	~40%
RB1290X2E	2 x 9 Ah	24 V	F2	$129.99	~46%
RB1280X2B	2 x 9 Ah	24 V	F2	$127	~45%
RB1270X2C	2 x 7 Ah	24 V	F2	$121	~42%
RB1270X2A	2 x 7 Ah	24 V	F2	not published	unknown
RB1260X2A	2 x 6 Ah	24 V	F2	$116.95	~48%
RB1290	1 x 9 Ah	12 V	F2	$55	~36%
RB1270B	1 x 7.2 Ah	12 V	F2	$50	~30%
APCRBC160	2 x 7 Ah	24 V	F2	$156	~55%
APCRBC158	1 x 9 Ah	12 V	F2	not published	unknown
APCRBC159	4 x 7 Ah	24 V	unverified	$524	unknown
RBC55	4 x 17 Ah	48 V	NB	$805	~70%
RB1270X4	4 x 7 Ah	24 V	F2	$264	~47%
RBC1500	2 x 7 Ah	24 V	F2	not published	unknown
APCRBC123	2 x 7 Ah	24 V	F2	not published	unknown
APCRBC157	Not published	24 V	unverified	not published	unknown
RB0690X2	2 x 8 Ah	12 V	F2	$110	unknown
RB1290X2D	2 x 9 Ah	24 V	F2	$142.99	~51%
RB1280A	1 x 9 Ah	12 V	F2	$53	~34%