# T490 Battery Life

## Hardware Baseline

- **50 Wh** internal battery (3-cell)
- Panel draws ~4-5W at typical brightness
- CPU TDP-up 25W, TDP-down 10W

## Real-World Estimates

| Scenario | Runtime |
|---|---|
| Idle, screen off | 10-12 hours |
| Light work (terminal, notes) | 7-8 hours |
| Dev work (editor, browser, kubectl) | 5-6 hours |
| Browsing (10+ tabs, video) | 4-5 hours |
| Compiling / heavy CPU | 1.5-2 hours |

## TLP Configuration

`modules/t490.nix` configures:
- `powersave` governor on battery, `performance` on AC
- Turbo disabled on battery
- CPU capped at 40% max frequency on battery (~1.7 GHz)
- WiFi power saving on battery
- PCIe runtime PM (auto on battery)
- Intel GPU frequency limits (300-600 MHz on battery)

### Battery Health Thresholds

Lenovo Battery Team recommendations — configured in `modules/t490.nix`:
- **Start charging** below 40%
- **Stop charging** at 80%
- Thresholds persist in firmware (survive reboots without TLP)

This dramatically extends battery lifespan. Don't leave plugged in at 100% for days.

## CPU Throttling Fix

Intel Whiskey Lake CPUs have a bug where BD PROCHOT fires spuriously, locking the CPU at 400 MHz. The nixos-hardware T490 module enables `services.throttled` (erpalma/throttled) — this is mandatory.

**Skip thermald** — it conflicts with throttled. `services.thermald.enable = false` is set in `modules/t490.nix`.

## Additional Tweaks

- `pcie_aspm=force` — force PCIe power saving
- `i915.enable_rc6=7` — max GPU power saving
- `noatime,nodiratime` — reduce disk writes
- **zram swap** at 50% of RAM — faster, saves NVMe writes

## Quick Wins (No Config Needed)

- Lower screen brightness (40-60% is plenty — biggest power draw)
- Disable Bluetooth when not in use
- Use S3 deep sleep (not s2idle)
- Close unused browser tabs