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How to Choose the Right Battery Size for a Security Panel
Written from the field, not a spec sheet: how to calculate the exact capacity you need, how to wire batteries together when one battery isn't enough, and why most new installs today should be lithium.
Don't estimate — calculate the exact size
The single most common battery-sizing mistake isn't picking the wrong chemistry — it's guessing the capacity instead of calculating it. If you size a battery on a rough guess and it comes up short, you won't find out until the power actually goes out and the panel drops before backup time is up. The fix is simple but often skipped on site: work out the exact amp-hour (Ah) rating your load and required runtime actually demand, then buy to that number — not to whatever's on the shelf.
Match the battery voltage to what the system actually supports
Before capacity, check voltage. Every panel, NVR, or inverter is built to run at a specific voltage — commonly 12V, 24V, or 48V — and the battery bank has to supply exactly that, not something close to it. This is where a lot of new technicians get tripped up in the field: they have the right total Ah on paper, but wire the batteries together the wrong way and either don't reach the voltage the system needs, or reach it but lose the capacity they were counting on.
There are only two ways to combine batteries, and they do different jobs:
| Goal | Wiring | What changes |
|---|---|---|
| Increase voltage | Series | Voltages add up; amp-hour (Ah) capacity stays the same as one battery |
| Increase capacity (Ah) | Parallel | Voltage stays the same; amp-hour (Ah) capacity adds up |
For example: if the system needs 48V and you're working with standard 12V batteries, four of them wired in series gets you to 48V (12V + 12V + 12V + 12V). If instead you need more runtime — more amp-hours — at the same voltage the system already uses, you wire batteries in parallel instead; the voltage stays exactly where it was, but the total Ah capacity adds together. Series for voltage, parallel for capacity — mixing that up is one of the most common battery-wiring mistakes technicians make early in the field, and it's worth double-checking on every install rather than assuming.
Why lithium (LiFePO4) is usually the better choice now
For most new installs today, lithium (LiFePO4) is the stronger option over lead-acid or AGM. It's effectively maintenance-free — no periodic watering or equalizing charges to manage — and it tolerates a much deeper discharge without the shortened lifespan that punishes lead-acid batteries. The one thing worth keeping in mind is temperature: keep lithium batteries at roughly room temperature where possible, since extreme heat or cold has a bigger effect on lithium performance and long-term health than it does on lead-acid. Outside of that, the upgrade is usually simple for backup power that gets cycled regularly, once the existing charger and the device's charging circuit are confirmed compatible (see the note on chargers and the BMS below).
Before swapping out lead-acid: check the existing charger, and the charging circuit of the device the battery powers, against the lithium battery's datasheet. Canbat's manual notes that flooded lead-acid charging algorithms are often set higher than LiFePO4 voltage requirements, which can make the battery's built-in BMS disconnect, and Power-Sonic lists conditions (no desulfation mode, and specific bulk and float voltages) for using a lead-acid charger with its lithium batteries. The BMS protects the battery, but Canbat advises treating it as the last layer of defence rather than the first, and a battery that has disconnected can read 0 V, which some lead-acid chargers cannot recover. Also check the datasheet's charging temperature limits: Canbat states that its standard LiFePO4 batteries can be charged between 0 °C and 45 °C and that the BMS stops charging outside the limits, and limits differ by model. Sources: Canbat lithium charging instructions (manufacturer PDF), Power-Sonic: how to charge LiFePO4 batteries.
The bottom line
The reliable order of operations on any backup-power job: calculate the exact Ah your load and runtime require, confirm the voltage the system needs and plan your series/parallel wiring to hit it without losing capacity, and then choose lithium where the budget allows for the lower maintenance and deeper safe discharge. Skip the calculation step and every decision after it is built on a guess.
Related tools
Sizing a battery from a watts/amps load and target runtime? Start with the Amp Hour Calculator. Sizing backup specifically for an alarm panel, NVR, or PoE switch with standby-plus-alarm current? Use the Battery Backup Calculator — though if it's a PoE switch, it's worth running the PoE Budget Calculator first, since a switch that can't power its cameras in the first place isn't a backup-sizing problem yet.
Already have a battery and want to know how long it'll actually run your load? Try the Battery Amp Hour Calculator instead. And if 12V cameras are fed over a long cable run, a correctly sized battery still won't help if the cable drops too much voltage before it reaches the camera — check that with the Voltage Drop Calculator.