Low battery alerts

Battery devices die quietly. A contact that last reported 47% three weeks ago is already empty; a coin cell that chatters unavailable is worse than one that still has a number. This workflow walks every battery sensor Home Assistant knows, keeps the ones at or below your cutoff (default 15%) or stuck unavailable/unknown, and sends one grouped notification — not a page each time a sleepy node wakes.

Entity ids stay in blueprint inputs. Do not publish a live inventory of which rooms still have coin cells.

If you are building the contact yourself, the battery reed door sensor pack already exposes a voltage entity this scan can pick up. Complements offline devices report for nodes that never came back after an outage.

What problem it solves

You want a single “replace these cells” list on a weekday morning, plus a way to ignore the phone at night, without writing one automation per sensor and without paging on every 1% twitch.

How it works

1. Discover — the blueprint selects entities with device class battery (percent sensors and “battery low” binaries). You do not maintain a hand list unless you want a custom group with a stricter cutoff (shade motors that are dead at 50%, for example).
2. Threshold — any percent at or below the warning level (pack default 15%) is a hit. unavailable and unknown are hits too; a node that stopped reporting is more urgent than 14%.
3. Excludes — skip hidden entities, skip specific sensors, skip labels you use for “ignore this cell.” UPS units that sit at 80% by design belong here.
4. Quiet hours — if a manual button run lands inside the quiet window, skip the phone push (the persistent UI card can still update). The weekly roll-up is scheduled outside that window, typically a weekday morning.
5. Weekly roll-up — one notify with friendly names (and optional area / percent). Actionable Companion buttons can drop the list onto a to-do. A later run with the same notification_id replaces the persistent card.

A 1% bounce around the cutoff will not spam you: the scan is periodic, not a numeric_state trigger on every sensor.

Hardware notes

• No extra hardware. This watches battery entities you already have. Zigbee, Z-Wave, ESPHome ADC, and BLE all look the same once they are a % sensor or a low-battery binary.
• Notify. Companion (notify.mobile_app_your_phone) for the phone; persistent notification for the desktop. Pushover works if you point the notify input at it.
• Sleepy ESP32 reeds. A deep-sleep contact that only publishes voltage on wakeup will look unknown between boots. Either exclude it and trust the on-device low-battery binary from the battery reed pack, or give it a timed wakeup long enough that the weekly scan usually catches a fresh reading.

Snippet

The pack ships a blueprint. Inputs replace real entity ids:

trigger:
  - platform: time
    at: !input weekly_time
    id: rollup
  - platform: state
    entity_id: !input check_button
    id: manual
condition:
  - condition: or
    conditions:
      - condition: trigger
        id: rollup
      - condition: not
        conditions:
          - condition: time
            after: !input quiet_start
            before: !input quiet_end
action:
  - variables:
      low: >
        {{ states.sensor
           | selectattr('attributes.device_class', 'eq', 'battery')
           | selectattr('state', 'lt', threshold)
           | map(attribute='name') | list }}
  - service: notify.notify
    data:
      title: "Low batteries"
      message: "{{ low | join(', ') }}"
  # excludes + unavailable + persistent card: full blueprint in the pack

Setup outline

1. In Developer Tools, filter device_class: battery and glance at real percentages so 15% is sane for your mix (CR2032 vs LiPo vs NiMH).
2. Create the optional input_button and a to-do list if you want the action button.
3. Import the blueprint. Set threshold, weekly time, quiet hours, notify service, and the first excludes (UPS, always-charging tablets).
4. Run from the button at a time outside quiet hours. Confirm: one grouped push, persistent card, quiet-hours button run stays silent on the phone, excluded entities stay off the list.

Troubleshooting

• Everything is “low.” The entity is voltage (2.8) not percent (28), or the integration reports 0–1. Exclude it or wrap a template that scales to 0–100 before the scan.
• A binary “battery low” never appears. Some integrations use on for low, others invert. The pack treats on as low; invert in a template helper if your device is backwards.
• Night pages. The weekly time sits inside quiet hours, or you used a naive after that does not wrap midnight. Move the roll-up to morning; keep the pack’s wrapping time condition.
• Same device listed twice. Percent and a low-battery binary. Exclude one, or you will replace two cells that are the same coin.

Credits

Based on Blacky’s community blueprint Low Battery Notifications & Actions. This write-up is an original overview of the house-wide threshold-plus-roll-up pattern.