Battery Considerations for the Garmin Reactor 40 Kicker Autopilot

Battery Requirements for the Reactor™ 40 Kicker Autopilot

The Reactor 40 Kicker requires larger batteries than other autopilots because it trolls at low RPM or slow speeds for long days. The Kicker engine running at lower RPMs (8 to 25hp) will not output sufficient power to maintain the battery charge. Main engines with higher amp output are designed for short periods of time. 

Most boat setups require the batteries to be fully recharged before each trip, whether a smaller electrical boat operating with a 75AH dual-purpose, deep cycle battery or a larger electrical boat with a 200AH battery. The remainder of this FAQ will discuss why recharging is necessary.

Typical Batteries in Boats

Starter Battery

• Power rated cold cranking amps (CCA) or marine cranking amps (MCA)

• Optimized for large power draw over a few seconds (starting an engine)

• Not designed for power draw over longer periods

These batteries do not have an AH (amp hour) rating. Using a starter battery for this purpose will age the battery faster and deliver marginal or poor performance. 

Dual-Purpose Battery

• Power rated by CCA or MCA and AH

• The AMP hour rating tells how many amp can be drawn from this battery over hours, at a maximum rate

Example: 800 CCA / 75AH @ 20A. The battery will supply up to 20 amps per hour for around 3.5 hours - when new. 

Deep Cycle Battery

• Power rated by Ah (Amp hours) 

• Optimized for power draw over longer periods

The Amp hour rating lists how many amps are drawn from the battery over hours, at a maximum rate. Example: 100Ah @ 20Amps will supply up-to 20 Amps per hour for around 5 hours- when new. 

Reactor 40 Kicker Autopilot Power Usage

Reactor 40 Kicker will draw around two amps per hour in calm conditions. As it works harder in waves and turbulence, the amp draw will grow higher up to 15A for one second each time it drives the rudder up to a stop. Setting “Min RPM” to 1500 helps reduce high idle activity, conserving some power.

Issues Caused by a Low Battery

When battery power is low, several issues can occur with the Reactor 40 Kicker:

• ECU Low Voltage warning

• Lost Speed Source error

• Loss of throttle control

• ECU Lost error along with autopilot no longer steering (stuck in turn)

Typically, this looks like the autopilot was performing just fine for some hours, and now it has some of the issues noted above. If running the main motor makes the problems disappear, the battery will likely be the problem.

Suppose these errors occur immediately after engaging the autopilot with the main engine running. In that case, another problem may be, such as throttle controller cable damage, wiring, or connector issues on the ECU power cable.

Measuring the voltage of a battery when lightly used will not rule it in or out as a problem. 

A more significant draw on a weak battery can cause the voltage to dive down rapidly. The voltage may recover afterward. A large draw can be the autopilot driving the rudder against the port or starboard stop. This voltage spike can happen quickly enough that the ECU doesn’t see it in time and resets. 

It can also result in just the throttle actuator restarting (lost speed source and loss of throttle control).  

Estimating Proper Battery Capacity

• 12-volts

• How many hours are needed between charging on shore (this will be the minimum amp hours capacity of the battery)

• Add up the power usage from electronics (in amps per hour)

• Consider the kicker outboard charging output (in amps – per hour)

• Add some additional capacity to allow for loss due to aging and charging mistakes (say 25% more capacity)

Example #1 – 22’ boat with a Yamaha 9.9hp kicker, a Yamaha 150hp main engine

Freshly charged house battery that is new, no charge from kicker

The electronics will draw around 6A per hour. The batteries may power the electronics for up to 12 hours.  

With the kicker motor running and outputting charge to the battery

The kicker motor is used during trolling at around 1500 RPM, with full throttle at 6000 RPM (so one-quarter of full throttle). The alternator for a Yamaha 9.9hp outputs 6A at full throttle. Let’s estimate an output of 1.5A at trolling speed, with 6A power usage by electronics and the outboard supplying 1.5A, which leaves a 4.5A draw on the battery.   This scenario will power the electronics for 16 hours (starting with a freshly charged, new battery). If the battery is not put onto a charger, it will run out of power after 16 hours of trolling (3 days).

Freshly charged old battery and kicker at trolling speed

 A battery loses capacity as it ages. It can be damaged by overcharging or running it below a safe voltage level. Let’s say the battery in the above example is now six years old. It now has half the capacity, 40 amps. With the kicker at trolling speed, we will use 4.5A per hour from the battery. The battery will power the electronics for 8 hours (starting with a fresh charge).

This house battery is the minimum size for this setup.

Example #2 – 26’ boat with Merc 15 and Merc 250hp main

The boat has two 12v batteries. One starter battery (800 MCA) that is reserved for starting the motors. One deep cycle battery (75Ah @ 20A) for the house, meaning all accessories including the electronics. 

The Merc 15 EFI engine outputs up to 4A at idle, producing a battery draw of 3 to 16 amps per hour.

Freshly charged new battery (75Ah capacity): Typical 75Ah/3A = 25 hours. Max 75Ah/16A = 4.5 hours. This house battery does not have enough power.

Freshly charged old battery (40Ah capacity): Typical 40Ah/3A = 13 hours. 40Ah/16A = 2.5 hours. This type of battery does not have enough power.

The house battery for this boat should be:

• 12v

• Two days' worth of trolling, starting with a freshly charged battery. 10 hours.

• Size it for the max power usage. 20 amps per hour

• The kicker engine outputs 4A per hour, leaving 16A per hour to draw from the battery.

• 10 hours *16 amps/hour = 160Ah (amp-hours)

Add 25%: 

• 160Ah x 1.25 = 200Ah

Remember, it must be recharged on shore power after no more than 10 hours of trolling.