Installing a lithium house bank on a boat sounds intimidating until you realize most of the work is just wiring â and there is really only one connection point where things get tricky. Today I am walking through a LiTime lithium battery install paired with a DC-to-DC charger â the combination that finally made this house bank system safe to run alongside the traditional lead acid starters. LiTime sent me this battery after I reached out looking for a new power solution, but the principles below apply to any lithium upgrade on a boat that still runs lead acid for starting duty. Before we touch a single cable, let me explain why lithium is the future of boating.
Why Lithium
The first and most important reason is power. Lithium batteries can use almost all of their energy capacity without a drop in voltage. For comparison, the old lead acid batteries only use about half of their power reserve before voltage drops to an unusable level. That means this one battery has twice the amount of energy storage as two 8D lead acids combined. The second reason is size and weight. This is the mini model, which means it is 30 percent smaller than other 300 amp hour lithium batteries and about half as light as three 100 amp lead acids. And the last reason is right there on the label next to the word mini â the word smart. This battery has a built-in battery management system that keeps it from damaging itself, plus Bluetooth so you can see and monitor its use from your phone.
Why You Need a DC-DC Charger
In my case I am adding the lithium battery as its own house bank system and keeping the two lead acid 8Ds for the starting batteries. The two different types of batteries have different charge and discharge profiles, and they are not going to get along with each other. That difference in how lithium holds voltage throughout while lead acid drops off means directly connecting the two types would cause a lot of problems. We really want to avoid connecting the alternators directly to the lithium battery. Luckily there are a lot of good resources online for explaining how to do this, many from the RV and vanlife community â all the concepts are the same. The solution is to completely separate the two battery systems and connect them through a DC-to-DC charger. That charger acts as the only connection between the two systems, allowing both to operate independently while staying charged.
The Charger
The charger I am using is LiTimeâs 12 volt 40 amp DC-to-DC charger with MPPT. I like this charger for a few reasons outside of the fact that it was provided with the battery. First, it is a fair size â pretty small, and I think everyone will be able to find a place to mount it. Second, using the same brand charger with your battery just makes sense. If you use the same brand equipment, nothing should ever really give you trouble because it is all tested for their products. And last, this charger comes with MPPT built in. For those unfamiliar, the MPPT is usually a separate system you have to buy in order to hook up solar panels. In this case the solar connection is integrated into the charger itself, and it will automatically switch between solar and alternator power, prioritizing the alternator when the engines are on.
The Install
As I wired my entire boat myself five years ago, I know exactly which cables power the whole electrical system. The only thing not connected to the system is the bilge pumps, which I am leaving directly connected to the 8Ds for now. The existing cables turned out to be shorter than I needed, so I had to measure and cut new cable. I also had to crimp different lugs because the terminals on the lithium battery are a bit smaller than the old lead acids. With the battery box in place and the new house system initiated, I left the negative terminal disconnected and moved on to the DC-to-DC charger.
The charger comes with all the necessary connections and nice quick disconnects. But I added two more things on the recommendation of the wiring diagram â circuit breakers before and after the charger. The charger is rated at 40 amps and recommends an input breaker of 60 amps and an output breaker of 50 amps. You will also notice I am not installing a battery switch at this time. That is because I have a DC breaker panel that everything runs off of, and I am hoping that when it is shut off I will not have any parasitic draw. I also intend on adding solar soon after this project, and if I add a battery switch near the battery it would disconnect it from the charger. If it becomes a problem down the line, I will add one. But for now I am just going to monitor the situation.
Wiring It Up
The charger has four main connections that consist of seven wires. The first pair is the positive and negative of the MPPT system â that is for solar, something I will deal with at a later time. The second is an accessory cable that hooks up to a power source in case you have small alternators. I have traditional dumb alternators, so the charger itself reads when my alternators are producing voltage to the starting batteries and then charges the service battery on its own.
To wire everything correctly, you actually start with the output side first. Take the positive output and run it to your positive bus bar so it connects to your entire system and charges the service battery. The negative output goes to the negative bus bar before any shunt or voltage monitor you have. You want to do the output side first because the service battery provides power to the charger and lets you select the battery type before the input side starts charging. Once the output is connected, take the positive input wire through the 60 amp breaker to the starting battery switch. Then connect the negative input directly to the terminal on your starting battery. I made a huge mistake here â I tried connecting my input negative to the same bus bar as the output negative, assuming it would all be the same. The charger would not turn on or read the proper voltages. It needs the input side as directly connected to the starting battery as possible so you are not losing any voltage over distance or cable connections.
With everything in place there is one last feature worth mentioning â the reverse charge button. You can hold it down in case your starting battery bank gets too low. If it is anywhere between 3 and 12 volts, you can actually push power from the service battery back into the starters to get your engines running. My goal is to get to the point where the boat can run any piece of equipment indefinitely and be monitored remotely, and the next project on my list is adding a dedicated Victron battery monitor so I can see exactly what this house bank is doing in real time. Big thank you to LiTime â check them and their batteries out. You will be surprised at how much power they can fit in these small things. Smooth sailing.
If you want real-time visibility into a lithium house bank like this one, the [FUTURE LINK: Why Every Boat Needs a Victron Battery Monitor Installed] writeup covers exactly that piece.
