Power System
Goal: simple, reliable power for the Espar heater, roof fan, and small DC loads; fast alternator charging; clean install; solar-ready later; optional AC.
Options
1) Factory-style Mercedes Aux AGM (under-hood, OEM kit)
Core components
- Mercedes auxiliary battery tray/harness/relay kit — $400–$600
- 95–100 Ah AGM (Group 49/H8) — $250–$350
- Optional Orion-Tr 12/12-18A for smarter charging — $175
- Small DC fuse block, wire, lugs — ~$125
Total: ~$725–$1,100
Capabilities
- Alternator charge via factory relay (or 18 A DC-DC if added)
- Usable energy: ~50 Ah ≈ ~0.64 kWh
- Heater runtime: ~1–2 nights
- Minimal cabin space; OEM isolation
Pros
- Simplest hardware; OEM look and mounting
- AGM charges fine in cold
Cons
- Low usable capacity for deep cycling
- Fewer upgrade paths than lithium
Looks
- Clean OEM under-hood appearance; minimal interior impact
2) DIY Victron LiFePO₄ (marine-grade, fixed install)
Core components
- 12 V 100 Ah LiFePO₄ (self-heating, Bluetooth optional) — $320–$595
- Victron Orion-Tr Smart 12/12-30A DC-DC — $220
- Victron SmartShunt 500 A — $130
- Blue Sea ST Blade 12-cct (5026) — $55
- Blue Sea 285 breaker 100 A — $55
- Blue Sea 7720 MIDI block + 40 A fuse — $45
- Blue Sea 6006 battery switch — $35
- Ancor tinned wire, lugs, fuses, heat-shrink — ~$170
Total: ~$1,350–$1,450
Capabilities
- Alternator charge: 30 A (~360 W) while driving
- Usable energy: ~80–90 Ah ≈ 1.0–1.15 kWh from a 100 Ah pack
- Heater runtime: ~3–4 winter nights (heater only)
- Full 12 V distribution now; easy to add loads later
- Solar: add MPPT later (e.g., Victron 100/30 or 100/50)
Pros
- Efficient DC path, low losses
- Works below freezing with heated cells
- Serviceable, standard parts
Cons
- More install time and wiring
- AC requires adding an inverter
Looks
- Functional, exposed components and cabling
3) Bluetti AC200L + D40 + Charger 1 (chosen, portable/hybrid)
Core components
- Bluetti AC200L (2,048 Wh, 2.4 kW inverter) — $1,199 (sale)
- Bluetti Charger 1 (≈560 W alternator charger) — $249
- Bluetti D40 (regulated 12 V up to 30 A) — $150
- 6-way marine fuse block + ground bus — $25
- 8–14 AWG marine wire, MIDI fuses, lugs, loom — ~$75
Total: ~ $1,700 all-in
Capabilities
- Alternator charge: ≈560 W into AC200L while driving
- Regulated 12 V 30 A to a fuse panel (heater, fan, lights)
- Usable energy: ~1.6 kWh from AC200L’s 2.0 kWh pack
- AC: 120 V, 2.4 kW built-in, surge headroom
- Solar: dual inputs, up to ~1,200 W
Pros
- Plug-and-play; minimal wiring
- Strong built-in AC; easy portability
- Tidy footprint; quick to remove or service
Cons
- More conversion steps than a pure DC system
- LiFePO₄ charge limited near/below 32 °F → keep unit warm
Looks
- Sleek enclosed unit; modern consumer aesthetic
Note: AC200PL was dropped; Bluetti support confirmed it is not compatible with D40 in our use.
Decision Matrix
| Criteria | DIY Victron LiFePO₄ | Mercedes Aux AGM | Bluetti AC200L (chosen) |
|---|---|---|---|
| Parts cost (complete) | ~$1,350–$1,450 | ~$725–$1,100 | ~$1,700 |
| Usable energy | ~1.0–1.15 kWh | ~0.64 kWh | ~1.6 kWh |
| Alternator charging | 30 A (~360 W) | Relay or 18 A DC-DC | ≈560 W (Charger 1) |
| 12 V distribution | Full marine panel | Small panel | D40 → 30 A panel |
| AC power | Add inverter | None | 2.4 kW built-in |
| Cold-weather charging | Good (heated cells) | Excellent | Limited near 32 °F |
| Expandability | Add cells, MPPT, inverter | Limited | Bluetti expansion packs |
| Portability | Fixed | Fixed OEM | Portable/hybrid |
| Install complexity | Highest | Low | Low |
| Looks | Functional, exposed | Clean OEM | Sleek, integrated |
Outcome: AC200L + Charger 1 + D40 best matches our heater-first use, fast alternator charging, simple install, and clean look.
Notes and Safety
- Fuse within 7 in of any source (starter, battery, D40 out).
- Use tinned copper wire and adhesive heat-shrink lugs.
- Keep the alternator-charging path ignition-controlled to protect the starter battery.
- Verify torque on all studs; re-check after first trip.