# Calarin battery sourcing shortlist — 2026-04-12

## Goal
Pick a workable v1 battery direction for a MagSafe-mounted recorder that sits on the back of an iPhone.

User constraints now:
- attach to back of phone with MagSafe
- credit-card-ish / wallet-ish footprint is acceptable
- prioritize balance over perfection
- move quickly, but don’t lock in the wrong product shape

## Core conclusion
For this product, the right battery philosophy is:
- thin-and-long beats thick-and-compact
- area is cheaper than thickness
- a slightly larger flat slab on the back of the phone is better than a chunky bump

## Shortlist

### 1) Primary recommendation — 302540 class
Best current v1 direction.

Representative options:
1. 99Tech / Ecocell retail-style pack
   - class: `302540`
   - dimensions: about `3 x 25 x 40 mm`
   - capacity: `250 mAh`
   - connector: `JST-PH 2.0`, preattached
   - protection: yes
   - stock/price signal:
     - 99Tech: ~$6.95, 35 in stock
     - Ecocell: ~$6.95 inc GST, 379 in stock
   - notes:
     - turnkey and easy
     - normal-discharge battery, not high-rate
     - max charge current about `125 mA`
     - max discharge current about `250 mA`

2. LiPol Battery vendor-grade pack
   - model: `LP302540`
   - dimensions: `3.0 x 25.0 x 40.0 mm`
   - capacity: `260 mAh`
   - connector: none by default, 50 mm wires only
   - protection: yes
   - MOQ/lead time:
     - MOQ `5 pcs`
     - about `1 week` to ship if in stock
   - notes:
     - more flexible if we want custom connector or wire choice
     - less turnkey than the 99Tech/Ecocell route

Why it ranks #1:
- closest to the actual product goal
- thin enough to preserve the flat-back direction
- common enough to source without fully custom battery hell
- capacity is modest but acceptable for v1

Expected runtime at rough current assumptions:
- `250–260 mAh`
- around `7.1–8.7 hours` at `35–30 mA avg`

Verdict:
- best balanced v1 answer

---

### 2) Secondary recommendation — 302560 class
Good if we want more runtime by spending footprint instead of thickness.

Market signal:
- visible in search results and vendor catalogs
- not many clean retail turnkey listings with connector/protection already attached
- looks more like a vendor/custom-order class than a hobby-retail class

Expected shape:
- about `3 x 25 x 60 mm`
- around `300 mAh` class

Why it matters:
- very aligned with the MagSafe-back product concept
- buys runtime through area instead of chunkiness

Why it ranks #2 instead of #1:
- sourcing looks less clean
- the 60 mm length may be totally fine, but we should confirm comfort on the phone back before committing

Expected runtime:
- around `8.6–10 hours` at `35–30 mA avg`

Verdict:
- strong option if we want a flatter, more phone-accessory-like product and are okay with a little vendor wrangling

---

### 3) Interesting premium-thin option — 223439 class
Most interesting “actually thin” battery family found.

Representative vendor-style option:
- model: `LP223439`
- dimensions: about `2.5 x 34 x 44 mm`
- capacity: `250 mAh`
- protection: yes
- connector: vendor/customizable configuration available
- notes:
  - available from specialty LiPo vendors
  - more exotic than the 302540 retail packs

Why it matters:
- this is the most compelling “thin slab” geometry found so far
- could be excellent for a polished later rev

Why it is not the default v1 answer:
- more specialty-supplier flavored
- less obviously turnkey than 302540
- wider footprint may or may not feel better in the real industrial design

Expected runtime:
- around `7.1–8.3 hours`

Verdict:
- very interesting rev-B / premium-v1 path
- not the easiest first battery to bet on

---

### 4) Electrical bring-up fallback — 402030 class
Use only if we want the easiest possible sourcing and don’t want battery sourcing to slow electronics work.

Representative options:
1. PMD Way retail pack
   - class: `402030`
   - dimensions: about `3–4 x 20 x 30 mm` depending on listing / real pack thickness
   - capacity: `200 mAh`
   - connector: `JST-PH 2.0`, preattached
   - protection: yes
   - notes:
     - easy to buy
     - straightforward prototype battery

2. LiPol Battery vendor pack `LP402030`
   - dimensions: `4.0 x 20 x 30 mm`
   - capacity: `200 mAh`
   - connector: no connector by default, wires only
   - protection: yes
   - MOQ: `100 pcs` on one listing

Why it ranks below the thin options:
- shape is less aligned with a MagSafe-back product
- thickness is worse than the thin-cell direction
- runtime is also worse

Expected runtime:
- around `5.7–6.7 hours`

Verdict:
- okay for rapid electrical bring-up
- not the right product-shape battery if we already know the device belongs on the back of a phone

---

## Practical ranking for Calarin v1
1. `302540` — best balance, best starting point
2. `302560` — good if we want flatter + a bit more runtime and accept more sourcing friction
3. `223439` — most elegant thin-cell geometry, but slightly more exotic
4. `402030` — fallback only

## Recommendation
Lock this as the v1 direction:
- target battery family: `302540`
- stretch battery family: `302560`
- prototype fallback: `402030`

## Concrete next move
Use a two-lane plan:

### Lane A — product-shape truth
- source `302540` packs first
- confirm MagSafe-back footprint comfort
- model enclosure around a flat battery-first stack

### Lane B — don’t block electronics
- if 302540 sourcing gets annoying this week, buy a `402030` too
- use it only as a bring-up battery
- do not let it redefine the product shape

## My blunt call
If we buy only one class right now, buy `302540`.
That’s the cleanest v1 move.

If we want to hedge, buy both:
- `302540` for the actual product direction
- `402030` as a no-drama bring-up fallback