FitMyRC
Knowledge Base

Fitment Guides

Essential reference material for the RC hobbyist. Whether you are new to LiPo power or a seasoned basher, these guides cover the technical details of keeping your car running safely and efficiently.

Examples

Traxxas Slash 2WD VXL Arrma Typhon 3S Team Associated RC10B6.4 Losi Mini-T 2.0

Connector Compatibility

Matching your battery to your ESC.

The single most common reason for a battery return is ordering the wrong connector type. Unlike AA batteries, high-performance RC packs use specific plugs designed to handle massive amperage.

IC5 / EC5

The standard for Horizon Hobby brands (Arrma, Losi). IC5 is the "smart" version with a data pin, while EC5 is the "dumb" legacy version. They are physically cross-compatible. If your Arrma Kraton has an IC5 plug, you can safely use an EC5 battery.

Traxxas (TRX/iD)

Proprietary connector found on Slash, Rustler, X-Maxx, etc. The modern "iD" connector removes balance leads, integrating them into the main plug. While convenient, this makes using non-Traxxas batteries difficult without an adapter or soldering.

XT60 / XT90

The open-source gold standard. XT60 is common on smaller 1/10 crawlers and drones (up to 60A constant). XT90 is the larger sibling for 1/8 scale bashers (up to 90A constant). Extremely reliable and easy to solder.

Deans (T-Plug)

An older standard featuring two flat, perpendicular blades. While common on budget-friendly builds and older race buggies, it handles less current than modern XT or EC connectors and is harder to solder.

The Adapter Problem

We strongly advise against using adapters for high-current applications (3S and above). Every adapter introduces:

  • Resistance: More metal junctions mean more heat.
  • Failure Points: Adapters can melt or vibrate loose during a bash session.
  • Length: Adapters add 1-2 inches of wire length, which can make fitting the battery into a tight tray impossible.

Soldering is the best solution

If you find the perfect battery spec-wise but it has the wrong connector, soldering on a new plug is the superior fix. If you aren't comfortable soldering, your local hobby shop will often do it for a small fee.

Voltage Safety

Understanding 'S' ratings and limits.

Voltage is determined by the cell count. One LiPo cell (1S) has a nominal voltage of 3.7V and a fully charged voltage of 4.2V. We stack these in series to get 2S, 3S, 4S, etc.

You must NEVER exceed the voltage rating of your ESC.

2S
Standard 7.4V

The baseline for 1/10 scale touring cars, buggies, and crawlers. Safe for almost all hobby-grade RCs.

3S
Performance 11.1V

Common in Arrma BLX 3S line and Traxxas VXL. Significantly faster than 2S.

4S+
Extreme 14.8V - 22.2V

1/8 scale monsters like the Kraton 6S or X-Maxx. Requires specialized high-voltage electronics.

C-Rating Explained

The "C-Rating" represents the discharge capability. A 5000mAh 50C battery can theoretically discharge at 250 Amps (5Ah * 50C).

Fitment Tip: Unlike voltage, you can never have "too high" of a C-rating. A higher C-rating just means the battery can deliver power faster without sagging. However, higher C-rating batteries are physically larger and heavier, which may prevent them from fitting in your tray.

Low Voltage Cutoff (LVC)

LiPo batteries are permanently damaged if discharged below 3.0V per cell. Modern ESCs have a "Low Voltage Cutoff" that stops the car when the battery gets low (usually around 3.2V-3.4V).

Warning: If you are converting an older brushed car (like an old Tamiya or Traxxas XL-5) to LiPo, ensure the ESC has an LVC mode. If not, you must use an external LiPo alarm, or you risk a fire.

Measuring Trays

How to ensure physical compatibility.

The most frustrating part of the hobby is buying a battery that is 2mm too long. Manufacturers often list "battery compartment size" but fail to account for the cables sticking out of the battery pack.

How FitMyRC Calculates Fit

We use a sophisticated tolerance engine. We take the raw internal dimensions of the tray and apply a buffer (default 2mm length / 1mm width) to ensure you aren't jamming the pack in.

Self-Measurement Checklist

  • 1. Obstructions: Look for screw heads protruding from the chassis floor or strap buckles that intrude into the tray space.
  • 2. Cable Exit: Does the tray have a wall at the front? If so, a battery with wires exiting the end of the pack adds ~10mm to the effective length. Look for "Hardcase" packs with top-exit bullets.
  • 3. Expansion Height: Many Traxxas models support an "Expansion Kit" (taller battery strap bar). We track this in our database, but check if your car has this installed.

Soft Case vs. Hard Case

Hard Case: Encased in a durable plastic shell. Mandatory for most racing tracks and highly recommended for bashing where the battery is exposed (like in a buggy). Dimensions are very consistent.

Soft Case: Wrapped in shrink wrap. Lighter and smaller, but vulnerable to punctures. Dimensions can vary by 1-3mm due to puffing or manufacturing tolerances.

Battery Care

Maximize lifespan and safety.

LiPo batteries are high-performance consumables. Unlike the AA batteries in your TV remote, they require active maintenance. A well-treated LiPo can last 300+ cycles. A mistreated one can fail in a week.

Storage Charge (3.8V per cell)

If you aren't going to drive for more than 48 hours, put your charger in "Storage Mode". Leaving a battery fully charged (4.2V) causes internal resistance to build up, making the pack "punchless" and puffy over time. Leaving it empty (3.5V) risks it dropping below safe levels.

Balance Charging

Always plug in both the main lead AND the small white balance connector. This ensures every cell in the pack reaches the same voltage. An imbalanced pack is a fire hazard.

The 1C Charge Rule

Unless your battery specifically says otherwise, charge at "1C". This means 1 Amp for every 1000mAh.
Example: 5000mAh battery -> Charge at 5.0 Amps.

When to retire a battery?

Dispose of a battery immediately if:

  • It is physically "puffed" or swollen like a balloon.
  • It has a sweet, chemical smell (punctured cell).
  • One cell refuses to balance or drops voltage rapidly under load.

Never throw LiPos in the regular trash. Take them to a recycling center.