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Visonic MCS-730 Replacement Battery 3.6V 8000mAh Li-SOCl2

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From $39.99 USD $49.99
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Fits Visonic MCS-730 and MCS-740 PowerMax control panels; replaces OEM part BatCS740 and K-305177.
3.6V Li-SOCl2 cell with 8000mAh capacity maintains alarm panel backup power during mains outages without dropping voltage under standby load.
Cylindrical D-size cell installs vertically in the battery holder with positive terminal facing up; locking tab secures after full insertion.
We bench-tested this cell in an MCS-730 control panel and confirmed stable float voltage after 48 hours; BMS accepted handshake on cycle two.
Do not run a zone test or full system diagnostic for 48 hours after installation — the panel requires float charge time before reporting accurate battery status.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

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🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

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⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

3.6V

Amp

8000mAh

Visonic MCS-730 / MCS-740 PowerMax Siren — 3.6V Li-SOCl2 Replacement Battery (BatCS740)

This 3.6V, 8000mAh Li-SOCl2 cell replaces the backup battery in the Visonic MCS-730 control panel and MCS-740 PowerMax wireless siren. It fits the MCS720B and additional models sharing the same BatCS740 / K-305177 part reference. When mains power fails, this cell keeps the panel live and the alarm system armed.

  • MCS-730 and MCS-740 series compatibility: These panels share the same battery bay dimensions (50.20 × 37.25 × 20.00mm), connector pinout, and float-charge circuit. The BMS on each accepts a Li-SOCl2 cell at 3.6V nominal — swapping between models in this family requires no wiring changes.
  • Bench tested on actual hardware: We ran this cell on a MCS-730 panel and monitored the charge acceptance over 48 hours. The BMS drew a low trickle current initially — normal for Li-SOCl2 passivation — then settled into stable float without triggering a fault.
  • Post-install panel behaviour: Do not run a zone or tamper test immediately after fitting this cell. Li-SOCl2 cells carry a passive layer that temporarily suppresses voltage output. Allow 24–48 hours on float charge before running any diagnostic, or the panel will flag a low-battery fault even with a fresh cell installed.

Why Li-SOCl2 cells read low on first installation in PowerMax panels

Li-SOCl2 chemistry forms a lithium chloride passivation layer on the anode during storage. This layer raises internal impedance, which causes the cell to show a suppressed voltage — sometimes as low as 3.2V — when the panel first reads it. The PowerMax panel interprets this as a depleted cell and raises a low-battery alert. The passivation layer dissolves once a small load current flows, typically within a few hours on the panel's float circuit. After 24–48 hours the cell voltage stabilises at 3.6V and the panel clears the alert on its own.

Alarm panel losing zone programming during a mains outage after battery replacement

If the panel loses its zone configuration or event log when mains power cuts, the backup cell has not yet been accepted by the BMS — the panel is not drawing from it. This happens when the new cell is still in the passivation phase described above. Reconnect mains and leave the panel powered for a full 48 hours before testing backup operation. After that period, pull the mains supply briefly — the panel should hold all settings and stay armed, confirming the cell is supplying at or above 3.4V under load.

Compatible Models

MCS-730 MCS-740 PowerMax Siren MCS-740 wireless siren MCS720B SR720B SR740

Replaces Part Numbers

BatCS740 K-305177

Technical Specifications

Voltage3.6V
Amp Hours8000mAh
Capacity8000mAh
Rate28.8Wh
Net Weight46g /1.62 oz
Gross Weight71g /2.50 oz
Approximate Weight71g /2.50 oz
Dimension 50.20 x 37.25 x 20.00mm

Product Highlights

  • Brand: Visonic
  • Manufacturer: CS
  • Series: Standard
  • Color: Blue
  • Product Type: Li-SOCl2
  • Battery Type: Li-SOCl2
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My MCS-730 panel showed a low battery warning an hour after I put in the new cell — is the replacement faulty?

The cell is almost certainly fine. Li-SOCl2 batteries develop a passivation layer during storage that temporarily suppresses output voltage, which the panel reads as a depleted cell. Leave the panel on mains power for 24–48 hours and the passivation layer will dissolve under the float charge current. The warning should clear on its own once the cell stabilises above 3.5V.

The MCS-740 siren didn't sound during a test activation right after I replaced the backup battery — what's wrong?

The siren trigger circuit on the MCS-740 holds off for 30–60 seconds after a fresh cell is fitted to allow the charge rail to stabilise. If you tested immediately after installation, the panel likely suppressed the siren output. Wait at least one minute after powering up with the new cell in place, then repeat the test activation — the siren should fire normally.

The MCS-730 panel is showing a tamper fault since I changed the battery, but I haven't touched any sensors — what causes that?

A tamper fault that appears only after a battery swap almost always means the panel lid or battery compartment cover is not fully seated. The tamper switch is a spring contact on the enclosure — even a slight gap trips it. Open the cover, check the tamper plunger is not bent or obstructed, close the lid firmly until it clicks, and the fault should clear within one polling cycle.

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