# Battery upgrade

[![IMG_20260828_205917_438.jpg](https://wiki.hexadust.net/uploads/images/gallery/2026-08/scaled-1680-/zE6aX68ApYn2sqiJ-img-20260828-205917-438.jpg)](https://wiki.hexadust.net/uploads/images/gallery/2026-08/zE6aX68ApYn2sqiJ-img-20260828-205917-438.jpg)![IMG_20260829_130717_560.jpg](https://wiki.hexadust.net/uploads/images/gallery/2026-08/scaled-1680-/LKvxvsmvr82gqXA3-img-20260829-130717-560.jpg)

<table border="1" id="bkmrk-2x-stock-batter-upgr" style="border-collapse: collapse; width: 100%; height: 270.8px;"><colgroup><col style="width: 33.3333%;"></col><col style="width: 33.3333%;"></col><col style="width: 33.3333%;"></col></colgroup><thead><tr style="height: 29.4667px;"><td class="align-right" style="height: 29.4667px;">**2x**</td><td style="height: 29.4667px;">**Stock batter**</td><td style="height: 29.4667px;">**Upgrade battery**</td></tr></thead><tbody><tr style="height: 35.0667px;"><td style="height: 35.0667px;">**Model**</td><td style="height: 35.0667px;">[EREMIT 606090](https://www.eremit.de/p/eremit-3-7v-4-000mah-high-cap)</td><td style="height: 35.0667px;">[HXJNLDC 7565121](https://www.amazon.co.uk/8200mah-7565121-Lithium-Replacement-portable-7-5%C3%9765%C3%97121mm/dp/B091YCRQXL?th=1)</td></tr><tr style="height: 29.4667px;"><td style="height: 29.4667px;">**Size**</td><td style="height: 29.4667px;">90mm / 60mm / 6mm</td><td style="height: 29.4667px;">122mm / 65mm / 7.5 mm</td></tr><tr style="height: 29.4667px;"><td style="height: 29.4667px;">**Chemistry**</td><td style="height: 29.4667px;">Lithium-Polymer</td><td style="height: 29.4667px;">Lithium-Polymer</td></tr><tr style="height: 29.4667px;"><td style="height: 29.4667px;">**Capacity**</td><td style="height: 29.4667px;">14.8Wh (4Ah)</td><td style="height: 29.4667px;">30.34Wh (8.2Ah)</td></tr><tr style="height: 29.4667px;"><td style="height: 29.4667px;">**Nominal voltage**</td><td style="height: 29.4667px;">3.7V</td><td style="height: 29.4667px;">3.7V</td></tr><tr style="height: 29.4667px;"><td style="height: 29.4667px;">**Discharge max continuous**</td><td style="height: 29.4667px;">2A</td><td style="height: 29.4667px;">5A</td></tr><tr style="height: 29.4667px;"><td style="height: 29.4667px;">**Charging limit voltage**</td><td style="height: 29.4667px;"><span class="font-semibold" data-streamdown="strong"><span data-sd-animate="true" style="--sd-animation: sd-fadeIn; --sd-duration: 0ms; --sd-easing: ease-in;">4.25V</span></span></td><td style="height: 29.4667px;">4.2V</td></tr><tr style="height: 29.4667px;"><td style="height: 29.4667px;">**Mass**</td><td style="height: 29.4667px;">74g</td><td style="height: 29.4667px;">136g</td></tr></tbody></table>

- **Connector**: JST-PH 2.0mm (not included in upgraded battery) (see [this](https://www.aliexpress.com/item/1005008783240077.html?spm=a2g0o.order_list.order_list_main.47.d6f418027X56aB) and [this](https://www.aliexpress.com/item/1005005953658258.html?spm=a2g0o.order_list.order_list_main.34.d6f418027X56aB)) 
    - **Datasheet:** [ePH.pdf](https://wiki.hexadust.net/attachments/129)
    - **Max current**: 2 A
- Both batteries have protection ICs

## Charging chip - MP2650

- Datasheet: [MP2650GV.pdf](https://wiki.hexadust.net/attachments/126)
- 4V to 21V Operating Input Voltage (V<sub>IN</sub>) Range
- Up to 5A Configurable Input Current (I<sub>IN</sub>) Limit (Up to 45W Total Power)
- Up to 5A Configurable Charge Current (I<sub>CHARGE</sub>)
- Configurable Battery Charge Voltage Regulation (V<sub>BATT\_REG</sub>) Up to 4.5V/Cell
- Up to 5V/3A USB On-The-Go (OTG)

## Monitoring chip - MAX17320G20+

- Datasheet: [max17320.pdf](https://wiki.hexadust.net/attachments/127)
- Battery Health + Programmable Safety/Protection 
    - Overvoltage (Temperature Dependent)
    - Overcharge/Overdischarge/Short-Circuit Current
    - Over/Undertemperature
    - Undervoltage + SmartEmpty
    - Battery Internal Self-Discharge Detection
    - Ideal Diode Discharge During Charge Fault
    - Charging Prescriptions (JEITA)
    - Prequal Charge Control with CHG FET
- ModelGauge m5 EZ Algorithm 
    - Percent, Capacity, Time-to-Empty/Full, Age
    - Cycle+™ Age Forecast
- Precision Measurement Without Calibration 
    - Current, Voltage, Power, Time, Cycles
    - Die Temperature, 4 Thermistors ±1˚C
- Cell Balancing with Internal FETs
- SHA-256 Authentication 
    - Nonvolatile Memory for Stand-Alone Operation
    - History Logging, User Data (84 Bytes)

## Firmware

`pocket-reform-sysctl-fw/src/sysctl.c` `void charger_init()`

```c
  // 2A max charge current, assumes 4000mAh cells.
  mps_reg_limits.charge_current = 1<<5 | 1<<3;
  // set all current limits to 500mA (should always be safe)
  int current_limit = 1<<3 | 1<<1;
  mps_reg_limits.input_i_limit1 = current_limit;
  mps_write_buf(MPS_REGSTART_LIMITS, sizeof(mps_reg_limits.all_regs), mps_reg_limits.all_regs);
  mps_read_buf(MPS_REGSTART_LIMITS, sizeof(mps_reg_limits.all_regs), mps_reg_limits.all_regs);
  mps_write_byte(0x0F, current_limit); // Input Limit 2
```

- Charging current limit is 2A by default hard-coded in the firmware.
- Upgraded batter can go up to 5A and charger chip can also go up to 5A but PH connectors only do 2 A max so can't increase charging current.

## Upgrade battery holding brackets

- FreeCAD: [bat\_holder.FCStd](https://wiki.hexadust.net/attachments/130)
- STL: 
    - [mnt\_bat\_holder.stl](https://wiki.hexadust.net/attachments/132)
    - [mnt\_bat\_clip.stl](https://wiki.hexadust.net/attachments/133)

[![IMG_20260829_165742_590.jpg](https://wiki.hexadust.net/uploads/images/gallery/2026-08/scaled-1680-/qol0Uu4U6MtLODxC-img-20260829-165742-590.jpg)](https://wiki.hexadust.net/uploads/images/gallery/2026-08/qol0Uu4U6MtLODxC-img-20260829-165742-590.jpg)

[![2026-08-29-170852.png](https://wiki.hexadust.net/uploads/images/gallery/2026-08/scaled-1680-/ppigU7xXkQxbcmQT-2026-08-29-170852.png)](https://wiki.hexadust.net/uploads/images/gallery/2026-08/ppigU7xXkQxbcmQT-2026-08-29-170852.png)[![2026-08-29-170758.png](https://wiki.hexadust.net/uploads/images/gallery/2026-08/scaled-1680-/nb2ReKWJE8wJi1HE-2026-08-29-170758.png)](https://wiki.hexadust.net/uploads/images/gallery/2026-08/nb2ReKWJE8wJi1HE-2026-08-29-170758.png)