Your battery data stays yours.

Last updated September 24, 2026

MultiBMS does not require an account, ads, or analytics. Nothing leaves your house unless you turn on the optional, paid MultiBMS Pro remote access. This page says exactly what happens in each case.

Two ways to use MultiBMS

The app works over Bluetooth, and optionally through a MultiBMS Gateway: an ESP32 board you flash and place near your batteries. The gateway is read-only; it cannot send commands to your battery. Data is handled differently depending on what you turn on.

Free: the app, and your gateway on home Wi-Fi

• The app reads your batteries over Bluetooth, or your phone talks to your own gateway directly over your home network. There is no account and no MultiBMS server involved. We receive no data.
• Your Wi-Fi name and password go from your phone to the gateway over an encrypted Bluetooth link and are stored only on the gateway. The app does not keep the password.
• Phone-to-gateway traffic on your home network is encrypted with a key shared only between your phone and the gateway.
• On iPhone and Mac, the app asks for local network access. It uses it only to find and talk to your own gateway.

Pro: remote access (optional, $1.99 per month per gateway)

Pro is $1.99 per month for one gateway, $3.99 for two, or $5.99 for three, with a 7-day free trial. If you subscribe and turn on remote access, your gateway connects to our relay at relay.multibms.com, which forwards live readings between your gateway and your phone.

• What passes through the relay: the raw battery readings your gateway collects (voltage, current, temperature, cell voltages and similar), which pack they belong to, the gateway's identifier, firmware version, and online status. Your phone decodes them.
• What is and is not encrypted: the connection between your gateway and the relay, and between the relay and your phone, uses TLS (HTTPS/WSS). Battery readings sent through the relay are not end-to-end encrypted, so the relay server can technically see them. Setup and control traffic (Wi-Fi details, pairing, settings) is sealed end to end between your phone and gateway with AES-256-GCM and is never sent through the relay.
• What the relay stores: the most recent reading for each pack (so the app can show data right away when it reconnects), the gateway's identifier and last-seen time, a hash of the gateway's claim secret, hashed access tokens, an anonymous random install id, and your subscription status. It keeps no history of readings.
• What it does not store: your name, email address, phone number, location, or Wi-Fi name or password. There are no accounts. Access is tied to the anonymous install id and tokens, not a person.
• Payments: handled by Apple or Google. RevenueCat, a subscription-verification service, validates purchase receipts for us under its own privacy policy, using the anonymous install id. We learn whether a subscription is active, which plan, and when it ends. We never see your payment details.
• Deleting your data: removing a gateway in the app (with the option to delete relay data) deletes that gateway's stored reading and tokens from the relay and tells the gateway to forget its relay credentials. A factory reset of the gateway also clears it. If a subscription lapses, stored data is deleted after 30 days. You can also email [email protected].
• Where it runs: on our own server. Access tokens are stored only as hashes.

Optional Home Assistant (MQTT)

If you enter your own MQTT broker in the app, your gateway sends readings directly to that broker. They do not go through MultiBMS and we see nothing. Your broker credentials are stored on the gateway. This is read-only: nothing can write back to your batteries.

Siri and Shortcuts

The Siri shortcut reads the latest battery snapshot already stored on your iPhone and answers from it. The shortcut itself does not contact MultiBMS.

What the app accesses on your phone

• Bluetooth device data: device names, signal strength, and live BMS telemetry such as voltage, current, temperature, state of charge, capacity, cycles, and cell voltages.
• App preferences: saved devices, groups, display choices, ride profiles, polling interval, temperature unit, and alert thresholds, stored locally. BMS credentials and gateway keys are kept in the operating system's secure storage.
• Optional Watch sensors: if you enable Ride or Race, Apple Watch uses location and motion for speed, distance, and G-force. This stays on your devices.
• Purchase status: Apple or Google reports whether a skin purchase or Pro subscription succeeded so the app can unlock it.

What we never do

• No advertising identifiers, analytics, behavioral tracking, or ads.
• No selling of data, and no sharing with advertisers. Data goes only to the service providers named above (Apple, Google, RevenueCat) and where the law requires it.
• No location history. Some Android versions label Bluetooth scanning as a location permission; MultiBMS does not use it to build or store your location.

Storage and deletion

Everything the app stores lives on your phone and paired Apple Watch. Uninstalling MultiBMS removes it; operating-system backups and store purchase history remain subject to Apple or Google policies. Relay data is deleted as described under Pro.

Purchases and third parties

Skins are optional one-time purchases and Pro is an optional subscription. Apple App Store or Google Play processes the transaction under its own privacy policy. Core battery monitoring and the free gateway do not depend on either.

Bluetooth and location permissions

Bluetooth permission is used to scan for and talk to BMS hardware and your gateway. Apple Watch location and motion permissions are used only for Ride and Race features you choose to run.

Children

MultiBMS is not directed to children under 13 and does not knowingly collect personal information from children.

Changes and contact

This policy may be updated as MultiBMS changes. The date above identifies the latest version. Questions can be sent to [email protected].