How to install a second battery in a boat

Away from any hot or moving parts and as close to the main battery as possible. Use the mounting plate on the back of the VSR to mark and drill four holes, and secure the top right and lower left holes with the short screws.

Then, take the length of red cable with lugs at both ends, and measure out enough cable to run from the centre of the mounting plate to the positive terminal of your main battery. Follow existing wiring where possible and avoid hot or moving parts.

Cut the cable to the correct length and repeat this step this time to the positive terminal of the auxiliary battery. Fit the lugs to the bare ends of the cable by stripping away 15 millimetres of insulation and crimping them in place with the crimping tool.

Your secondary battery will need a solid earth as well. Take the 24 inch black earth cable and again secure to a factory engine ground or similar. The VSR can now be attached to the mounting plate using the two longer screws, and the positive cables may be attached to the main and secondary batteries. Then secure the negative terminals - first to the main battery, then to the auxiliary battery.

Use the cable ties supplied to keep your wiring neat and safe. If you want to test your new setup, you can do so with a multimeter. Start the vehicles engine and take a reading from the main battery. Once the voltage climbs above Properly securing the battery box to the boat is the most critical part of installing the batteries properly.

People in too much of a hurry, screw directly into their hull, which eventually leads to dry rot in the fiberglass core. Take the time and do this step correctly.

I installed four in each battery box. The first time I secured the boxes, I forgot to install the strap. I had to remove the box and reinstall with the strap underneath.

While I was at it, I squired some silicone sealant into the new holes to seal the screw holes and prevent moisture penetration. Since I only have one battery bank, I wired these two batteries in parallel. Once all the wiring was done, I installed the lids and tightened them down with the straps. The screws secure the box to the boat.

This ensures that the marine battery boxes comply with the horizontal force part of the coast guard requirements. The plastic lids comply with the part of the requirement of a non-conductive terminal cover, and the strap ensures that I meet the vertical force requirements.

Sounds simple enough! I was wondering, one of the assets to a battery box is to hold the battery acid if the battery started leaking. This is important with an aluminum boat in that battery acid eats aluminum. Is there a sealant that could be used on the four screw holes to make the battery box liquid tight? I imagine that standard silicon caulking would work for that. I think code discourages drilling mounting holes in boxes.

A lawn tractor battery won't give you a lot of capacity, are hard to get in deep cycle and would also be very dis-similar to the regular battery which could make charging with the alternator a problem.

I decided against it and replaced the existing battery and box with the largest one which fits into the space. If you run both bilge pumps directly to a big battery with separate fuses you are almost as well protected as with a standard and a small battery. It's not that we have large cruisers moored all year long Comment Post Cancel. Maybe OP's boat is moored. If it's moored a better way would be to hook up a bilge pump to a 12V power supply connected to the mains. As an alternative I'd just have a battery-in-the-box I'd place on the floor and hook up the pump when I leave.

With an additional battery you reduce your payload and have a heavy object right at the stern where you really don't want it in a I remember seeing a post on here where a owner added a second battery.