BT Cruiser Battery Upgrade for Boondocking - Space Limited

Converter Compatibility Analysis

You're absolutely right to worry about cramming more battery power into your BT Cruiser's limited space — choosing the wrong upgrade could leave you with less boondocking capacity than you started with. Your WFCO converter's charging profile (verify exact voltages in your manual) is designed for flooded lead-acid batteries and falls within acceptable ranges for LiFePO4 batteries, though it's not ideal for either chemistry.

For flooded batteries like the 6V GC2s, this profile works well. For LiFePO4 batteries, while functional, the absorption voltage is slightly low (optimal charging voltage varies by manufacturer - consult your battery specifications) and the float voltage is unnecessary since lithium doesn't require float charging. However, this won't damage the batteries - you'll just get slightly reduced charging efficiency.

Battery Option Breakdown

Dual 6V Duracell GC2 Configuration

Two 6V GC2 batteries wired in series will give you 12V with capacity varying by manufacturer (typically in the 200+ AH range). This represents a significant upgrade from your current 88AH. GC2 batteries are specifically designed for deep cycling and typically handle several hundred discharge cycles depending on usage and maintenance. They'll fit your space constraints when positioned correctly, though you'll need to verify exact dimensions.

The main advantages include proven reliability, lower upfront cost, and excellent compatibility with your existing charging system. Disadvantages include heavier weight, maintenance requirements (checking water levels), and sensitivity to deep discharges below 50% state of charge.

Single LiFePO4 Options

Both Redodo LiFePO4 batteries offer substantial benefits for boondocking. The 140AH unit provides more usable capacity than your current battery since lithium batteries typically allow deeper discharge than lead-acid (consult manufacturer specifications for safe discharge limits). The 165AH version gives even more capacity but pushes your budget limit.

LiFePO4 advantages include: no maintenance, faster charging acceptance, consistent voltage output throughout discharge cycle, longer lifespan (typically 2000+ cycles), and lighter weight. The main drawback is higher initial cost and the fact that your converter isn't optimized for lithium charging.

Space and Installation Considerations

Your 12"x15" tray with 11" height creates tight constraints. Standard Group 31 LiFePO4 batteries vary by manufacturer - verify exact dimensions before purchase. Two 6V GC2 batteries dimensions vary by manufacturer - verify exact dimensions for your space, so you'll need to arrange them carefully - possibly one behind the other rather than side by side.

For the 6V setup, you'll need to run a short jumper cable between batteries for series connection, then connect your main positive and negative leads to opposite ends of the battery bank. This creates 12V while maintaining the amp-hour capacity of one battery.

Performance and Value Assessment

For pure capacity per dollar, the dual 6V GC2 setup wins decisively. The dual 6V GC2 setup typically offers good value, providing 200+ AH of nominal capacity. However, usable capacity is only about 110AH due to the 50% discharge limitation of flooded batteries.

The 140AH LiFePO4 at $260 provides about 130-140AH of usable capacity - more than the 6V setup despite lower nominal rating. The 165AH version gives you roughly 155-165AH usable capacity for $350.

Consider your camping patterns when choosing. If you're plugging in every few days, the 6V setup works well. For extended boondocking (4+ days), the lithium batteries' deeper discharge capability and faster recharging provide significant advantages.

Charging System Optimization

Regardless of which battery option you choose, your charging strategy impacts performance significantly. The WFCO converter provides basic charging but isn't sophisticated. For better results with either chemistry, consider adding a properly sized solar system with an MPPT controller that can be programmed for your specific battery type.

If you go with LiFePO4, you might eventually want to upgrade your converter to one with lithium-specific charging profiles, but it's not immediately necessary. Many RV owners run lithium batteries successfully on standard converters for years.

My Recommendation

Given your budget constraint and space limitations, I'd recommend starting with the dual 6V GC2 setup. It provides the most capacity improvement for the lowest cost and works optimally with your existing charging system. This gives you immediate boondocking improvement while you evaluate your actual power needs.

If you find yourself wanting even more capacity or getting tired of battery maintenance after a season or two, you can always upgrade to LiFePO4 later. The 140AH Redodo would be my lithium choice - it provides excellent usable capacity at a reasonable price point while staying within your budget.

Before making any purchase, verify exact battery dimensions and weight capacity of your battery compartment. Also consider having a qualified RV technician inspect your electrical system to ensure all connections and fusing are appropriate for your upgraded battery bank.

Tools & Supplies You'll Need

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