How to Hook Up Two Batteries In a Boat

There’s nothing more satisfying than a smooth boat journey for boat owners. However, it isn’t uncommon to encounter harsh weather conditions or technical issues that impede the trip. 

While a sudden storm can leave you petrified, running out of battery isn’t any less terrifying. 

Your boat may break down during the journey due to a dead battery. In case you face such an issue, the catch is to remain calm and undertake a solution. 

Adding a second battery can come in handy and unlike a car battery, hooking one up is pretty straightforward. Stay with us as we reveal the secret sauce of it all. 

Supplies Required to Connect Dual Batteries In Your Boat 

You need to consider a few things before actually installing the batteries, from tools to supplies and installation factors. Here is the stuff you’ll need before hooking up the batteries to your boat. 

How to Hook Up Two Batteries In a Boat

A Second Battery 

The marine battery you need differs per boat power requirements. For instance, lighting, navigation systems, and other energy-consuming applications typically feature thick plates. This ensures that they provide reliable starting power and can tackle varying loads. 

Selector Switch 

Disconnecting the batteries enables you to handle the total amount of electricity on the board. Generally, they are utilized to connect and unplug electrical appliances from the main power outlet and keep the battery from draining. 

Black and Red 2/0 Marine Cable 

This marine cable is fine and features thin wiring inside its single strands. The design makes it incredibly flexible and enables it to function optimally in a moving boat. 

Besides, the tinned strands resist corrosion, and different colors make it easier to recognize the cable to attach for negative and positive interconnections. 

A Battery Box 

A battery box is meant to protect the battery. It keeps oil, water, and other foreign objects from making their way into the engine and damaging it. 

This is crucial if you have lead-acid batteries installed in your boat. These batteries may leak acid into your boat upon breaking down. 

2/0 Marine Crimped Cable Lugs

Make sure to connect the crimped cable end to a connector terminal portion. This is followed by compressing the wire to solder it.

Boatowners or engineers typically crimp the cable using the crimping pliers or other related tools. 

Heat-Shrinking the Cable-Lug Connections

Heat shrinking the wraps of the connector makes up for a protective battery connection seal. It features a material that shrinks on heating. Consequently, the firm closure keeps the terminals, wires, and connectors from water or corrosion of electrical devices. 

Terminal Caps for the Battery’s Positive Port

Terminal caps keep the boat’s battery from flashing or otherwise short-circuiting. The rubber, plastic, or other synthetic covers shield the battery from electrical equipment abrasion or water. 

Tools Needed to Mount the Batteries 

You’d need a few handy gears for a successful dual battery installation. These include:

  • A cleaning brush. You’ll need this brush to clean the rust from the terminal. Insert the brush and thoroughly clean the negative and positive ends of the battery. The tool may come in handy for cleaning the battery posts. 
  • Dielectric lubricant. This greasy liquid will keep your battery from abrasion and protect its terminals. It helps connect the batteries seamlessly. Therefore, it’s always good to have this tool in your battery box/tool kit. 
  • 10mm combination socket. Because you have to start the process by removing the battery, you’ll need a 10mm socket to detach it. Unfasten the 10mm bolt to unhook the battery clamps. 

Installation Factors to Consider

Savvy boat owners always keep an extra battery in their boats. It boosts their vessel’s performance and protects them against unexpected events. 

However, after preparing for the battery hook-up, you must consider a few critical factors. This will ensure a smoother battery installation and keep you from wasting your time. 

  • Space. You cannot add a second battery if you do not have enough room. Make sure you check the available space and build another battery section. However, adhere to the safety standards as you did for the first one. 
  • Wiring. Your second battery must be compatible with the first one to avoid power distribution problems. The circuit route lengths should be the same. Besides, the positive end of the old battery must be linked to it while the negative connection of the new one should be joined to it. 

Tips for Safe Handling 

Safety comes before anything else. Slight negligence when mounting the new battery might escalate the existing issues – especially if you’re stuck in the middle of the sea. 

Make sure you handle the process like a pro for a successful hook-up.  

  • Because batteries contain dangerous substances, coming into contact with them poses a risk. Therefore, you must ensure that the batteries are detached from the wires. You’ll avoid short circuits and other potential hazards through this simple step. 
  • Consider using the wires mentioned in the handbook and read the safety warnings before proceeding. 
  • The metal-to-metal connections must be in good condition. You can always take a look to see if they are clean. Besides, they must be waterproof and of the correct size. 
  • Do not forget to wear protective glasses and heavy-duty gloves during the installation.  
  • Boat engineers recommend using Nylock or Hex nuts instead of wingnuts for motor applications. Besides, it is always wise to firmly secure the lock washers. 
  • Keep the water handy in case of sudden acid spills. 
  • Avoid proceeding with the installation in an open flame. 
  • Use uninsulated gear cautiously as it may lead to a short circuit. 

Steps to Hook Up Two Batteries In a Boat 

Now comes the part you’ve all been waiting for. Follow the steps below for an effortless battery hook-up. 

Pick a Reliable Dual Battery Switch for Your Yacht 

You cannot choose a random switch and expect it to perform optimally. The boat’s battery switch must work for two batteries. Besides, it should be compatible with the existing one. 

Generally, a 250 amps rating works well for most outboards. 

You can also choose switches featuring locks to protect your boat against thefts. A few also contain field disconnection circuits to protect the alternator in case the batteries turn off while the motor is functioning. 

Attach the Second Battery of the Boat 

The installation must comply with local rules and requirements. However, wet-cell batteries must be kept in the battery box. 

The absorbed fiberglass batteries, on the other hand, do not need any packaging. Instead, they require brackets. 

Additionally, consider using a non-conductive covering to shield the battery’s positive terminals. 

Select an Appropriate Space for the Battery Switch 

Selector switches feature around 4-5 inches broad footprint. Therefore, you must select a spacious room. Standard regulations highlight that the switch should be close to the batteries and easily reachable. 

You can also flush-install it above the deck for a better appearance. However, you must protect it from outside stressors and foreign objects. 

Besides, make sure you wait until the positive wires attach to the connectors at the back. 

Wiring the twin battery switch is one of the most straightforward tasks. You can utilize dual switch batteries for the battery cells. This will keep your batteries running and prevent intrusion. 

Aside from that, you must consider a few other things. 

  • Ground the two batteries in the boat’s engine common ground when attaching them.
  • Join one battery to a separate ground wire and the second one to the other wire for appropriate installation 
  • See if the engine’s ground wire can transfer the current in both batteries. As such, a second connection to the new battery is recommended. 
  • The battery cells must properly fit into the terminal cover. 

Attach the Negative and Positive Cables 

Check for the “marine cable” imprint on all the insulating covers and materials. It will aid a proper connection of negative and positive cables to the terminals. 

Managing the petrol inboards and outboards with a 2/0 sized cable is advised. 

Now, plug the positive connections of both batteries to the back of the corresponding switch posts. Next, attach the engine’s positive wire to the switch’s output port and connect the output port to the additional positive wire. 

Connect Them 

You’ll need a crossover connecting the negative connections of both batteries to make them function optimally. Besides, attach the negative supplementary wire and engine negative cable lug to a negative battery port. 

Now, fasten all the terminal screws to secure them. This will complete the installation of the new battery and keep you from unexpected hassles on your journey. 

Closing Notes

Dead batteries can destroy the fun of your yacht journeys. Therefore, preparing beforehand is always a better idea. 

Installing an extra battery will come in handy in case the other battery breaks down and fails to function. Besides, as a pro boater, you must keep an auxiliary battery handy. It will help you avoid the trouble and chaos in the middle of the vast sea. 

Hopefully, our guide will help you understand each step of hooking an additional battery on your boat. 

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