Configured for volatile memory retention and RTC backup in ControlLogix chassis, the Allen-Bradley 1756-BA2 (also cataloged as 1756-BA2 Battery Assembly) supplies 3 VDC from a 1200 mAh lithium cell to 1756-L6x Series B processors during main power loss.

Catalog Identity

The 1756-BA2 is the lithium backup battery assembly for ControlLogix L6x Series B and compatible L7x CPUs. The /A suffix denotes the released hardware revision. It is not interchanged with 1756-BA1 (L6x Series A) or 1756-BATA. No configuration jumpers or daughter boards exist.

Hardware Specifications

Backplane Power Isolation & Firmware Lock

The 1756-BA2 draws no current from the 1756 backplane 5 VDC or 24 VDC rail; it is electrically isolated behind the processor's internal switching diode and ESM capacitor bank. While the CPU is energized the battery sits open-circuit. On VAC loss the cell backs up SRAM and the real-time clock only. No firmware, no EDS, no backplane scan impact. I/O density and communication velocity of the ControlLogix chassis are unaffected by battery state. Hot-swap is permitted only while controller power is present; the onboard capacitance covers the milliseconds of connector disengagement.

Ordering Information

• 1 x 1756-BA2 Lithium Battery Assembly with lead and polarized connector
• 1 x Date label sticker

Controller Bay Integration

• CPU Match: Insert only into 1756-L6x Series B processor battery slot. Series A requires 1756-BA1.
• Live Swap: Keep controller powered during replacement; removing battery on dead CPU loses user program and tag values.
• Orientation: Seat horizontally with arrow mark upward, connector fully latched.
• Disposal: Treat as lithium primary cell; do not incinerate, recharge, or discard in standard steel waste stream.

Frequently Asked Questions

Does the 1756-BA2 charge while the controller is powered?

No. The cell is a non-rechargeable lithium primary. The CPU provides reverse-current blocking; no charge circuit engages.

What triggers the processor BAT LED?

When cell voltage decays past the threshold, the CPU sets minor fault type 10 code 10 and lights BAT red. Replace within the window while power is maintained.

Can 1756-BA2 be used in an L7x without an ESM?

L7x controllers ship with 1756-ESMCAP supercap module pre-installed. BA2 is still supported as extended backup but is not the primary energy store on L7x.

Is backplane current budget affected by battery fitment?

Zero. The assembly never loads the 1756 chassis power supply. Backplane 5 VDC/24 VDC sums exclude this part.

What is the data retention time at 25 deg C?

Rockwell quotes roughly 5 years idle retention at 25 deg C after a fresh install. Above 40 deg C cabinet ambient, expect accelerated self-discharge and shorter interval.

Can BA2 and BA1 share the same connector footprint?

Physical plug shape differs by keying. Forcing a BA1 into a Series B bay or vice versa risks polarity mis-seat and controller-side diode stress.

Does removing BA2 reset the RTC?

If main power is also absent, yes. With VAC present, RTC runs off controller clock circuit and battery is bypassed.

Are there slot restrictions in the 1756 chassis?

Battery lives inside the processor module, not a 1756 I/O slot. The "7 slots" figure in distributor listings refers to chassis size compatibility, not battery occupancy.