# Calculate How Many Batteries are Needed for the BP52

The [VBX series](https://docs.verkada.com/docs/ACC-VBX-series-datasheet.pdf) is an advanced backup battery system for the [BP52 Alarm panel](https://docs.verkada.com/docs/BP52-alarm-panel-datasheet.pdf). VBX batteries utilize lithium iron phosphate (LiFePO4) chemistry, which significantly outperforms traditional sealed lead acid (SLA) batteries in terms of lifespan and energy capacity.

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### How many batteries do I need?

The BP52 has two integrated battery slots and supports up to two external dual battery enclosures, allowing for a total of six 200Wh batteries. To calculate the backup capacity needed for your system, add the power of all high-load devices connected to your system and multiply this number by the number of hours of backup time required.

Divide the battery capacity needed by the capacity of the ACC-VBX-200WH battery to determine the number of batteries needed:

**# of Batteries Needed** = K / 200Wh

Examples of connected devices and their power consumption are provided below:

A = 8.5W (panel idle mode)

B = 0.5W (cellular backup average power consumption)

C = 3W (expander average power consumption)

D = 4W (keypad average power consumption)

E = 6W (Security Camera - day mode average power consumption)

F = 10W (Security Camera - night mode average power consumption)

G = 8W (Intercom average power consumption)

H (Total power) = A + B+ C\*(# expanders) + D\*(# keypads) + E\*(# Cameras) + F\*(# Cameras) + G\*(# intercoms)

J = hours of backup you need

K (battery capacity needed)= H\*J

{% hint style="info" %}
**Example:** A site with a panel, cellular backup, two keypads, an expander, and two cameras can typically run for 12 hours with two VBX batteries.
{% endhint %}

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### **Battery capacity vs temperature**

A battery’s capacity is not impacted by higher operating temperatures, but batteries operating at lower ambient temperatures have reduced capacity.

Subtract 1% capacity for every degree operating ambient temperature below 20°C.

{% hint style="info" %}
**Example:** Operating temperature is 10°C

Battery capacity is \[100% - (20-10)%] \* 200Wh

\= 90% \* 200Wh

\= 180Wh
{% endhint %}

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### **Recharge Time**

A minimum system power of 20W is allocated to battery charging, though more power is made available to charge batteries if system loading allows.

Assuming a minimum charge power of 20W, a fully depleted battery will recharge in approximately 10 hours. Multiply 10 hours by the number of installed batteries for the time to completely recharge all batteries.

{% hint style="info" %}
**Example:** The panel operates at maximum load, and only 20W is available for charging. AC power is restored just before the four connected batteries are completely depleted.

Recharge time = 10h \*4 batteries = 40h
{% endhint %}

A maximum system power of 90W is allocated to battery charging, which may be divided between all connected batteries up to a maximum of 40W per connected pack

At maximum charge power, a fully depleted battery will recharge in approximately five hours.