Step 1: Determine Your Voltage Requirement

Aircraft electrical systems fall into one of three voltage categories, and using the wrong one is not a matter of suboptimal performance — it can damage avionics or fail to start the engine entirely.

Check your aircraft's Pilot Operating Handbook (POH) or maintenance manual for the electrical system voltage. If you see a 24V battery, you need a 28V DC GPU. The GPU delivers voltage slightly above the battery's nominal voltage to ensure current flows into the aircraft's bus rather than being backfed from the battery.

If your aircraft requires 400Hz AC power, you are looking at a frequency converter rather than a battery start pack. See our frequency converter directory for that equipment category.

Step 2: Calculate Peak Starting Current

Peak starting amps — the maximum current the GPU can deliver during the initial engine crank — is the most critical specification for start packs. If the GPU cannot deliver enough current to spin the starter motor at the required speed, the engine will not start properly.

For turbine engines, insufficient starting current results in "hot starts" — the fuel ignites before the turbine reaches adequate rotational speed, causing excessive temperature in the turbine section. Repeated hot starts cause cumulative damage that can require early overhaul, costing tens or hundreds of thousands of dollars. This is why GPU sizing is a maintenance decision, not a purchasing one.

How to find your aircraft's starting current requirement

The most reliable source is the aircraft maintenance manual, which specifies the starter motor current draw. If this is not readily available, the following general ranges apply — but should be verified for your specific aircraft and installed equipment.

Select a GPU with peak amps exceeding your aircraft's requirement by at least 20%. This headroom accounts for cold-weather capacity reduction, battery aging, and the voltage sag that occurs under heavy load. A GPU rated at exactly your aircraft's starting current will likely deliver marginal performance, especially in cold conditions.

Step 3: Assess Continuous Power Needs

If you only need the GPU for engine starts, peak amps is the primary specification. But many operations also need continuous power for avionics testing, software updates, cabin environmental systems, and crew training with engines off.

Continuous power is measured in sustained amps at regulated voltage — a fundamentally different operating mode from the short high-current burst of an engine start. A GPU with 2,000A peak starting capability might only deliver 50A continuous, or it might deliver nothing continuous at all if it is a pure start pack.

If you need both starting and continuous power, a combination GPU is the appropriate choice. These units provide battery starting capability when disconnected from mains, and continuous regulated power when connected.

Step 4: Factor in Connector Type

The physical connection between your GPU and your aircraft must match. The most common connector types are the NATO-standard 3-pin oval connector (Cessna, many military aircraft), the round Piper connector, and 400Hz AC power receptacles for commercial aircraft. Using the wrong connector requires adapter cables, which add resistance and potential failure points.

Our aircraft-specific pages list the connector type for each model we cover.

Step 5: Consider Portability and Environment

A maintenance shop with a dedicated hangar position has different requirements than a line service operation moving GPUs between aircraft on a ramp, which has different requirements again from a helicopter operator carrying a GPU onboard to remote locations.

For weight-critical operations, lithium chemistry reduces GPU weight by 40–50% compared to lead acid. See our Lead Acid vs Lithium analysis for a detailed comparison.

For operations in extreme environments (temperature, humidity, salt air, dust), look for GPUs with IP-rated enclosures and environmental protection specifications that match your operating conditions.