Changing to a Lithium House Battery

[drewsbu]

Hey everyone! I did this swap a while ago but figured I would share in case anyone was considering doing the same or curious. I did this because I the stereo would last maybe 30 minutes with the boat off. My boat came with 2 FLA starting batteries so not too surprising. I did a bunch of research on different battery setups and decided to go with a 230Ah LiFePo battery. I did this because I spend a good amount of time at anchor with engine off, and I keep my boat at a stack marina so I have no way to charge the battery other than the alternator or taking it off the boat and bringing it home.

With this setup the house battery can’t be directly hooked up to the alternator, it requires a dc-dc charger. Works similar to an ACR. Because of this I also changed the battery switch from a 1/2/all/off to on/off/combine as the old switch doesn’t really work with this setup, and it also makes it so I don’t have to change the switch over when floating.

 

Here’s what I did:

Remove old batteries, unscrew the panels covering the switch, wiring by the switch, and the amp board. Take out old battery switch 

Install new battery switch and move wires to new spots – I re-used all the old wiring so didn’t run anything new. I ran the thick cable from the engine and the starting battery on the battery 1 side, and the 2 red cables going from the stereo and helm power distribution and a cable back to the house battery on the battery 2 side. The picture shows how the new switch is wired up.

Install DC-DC charger – I decided to put this on the amp board. It fit best closer to the helm so that’s where I put it. Luckily I got big enough gauge wire to make this run. For power wiring to the charger I ran it from the starting battery behind the amp board. Installed a 60A fuse right by the battery. For the wiring from the charger to the lithium battery I just ran this along the amp board instead of drilling a hole and running it behind, like the factory wiring. There is a 50A fuse inline and some screw in cable clamps keep the wiring neat. I used a 40A charger as to not strain the alternator too much, I still have the stock one. 

I mounted the lithium battery where the old battery #2 was, moving the mounting brackets a bit so it stuck out less into the observers compartment.

Last step was some re-wiring of the negatives. I mounted a negative bus bar and ran them all to that. 

Last thing I had to do with this charger was wire the sense line, which tells the charger when to turn on. I didn’t want to dig into the dash to tap into the ignition circuit, so what I did was buy a cheap ACR and used that for the sense. Easy solution to avoid splicing and running long wires. One unintended advantage of this is that the alternator voltage only gets high enough to activate the ACR when the engine is above idle, so it won't drain the starter battery to charge the house battery. 

Overall not too difficult of a swap and the end result is pretty great, a bit overkill actually. I didn’t install any type of charge monitor but based on the charge time with my 20A home charger 4 hours of floating with music at mid to high volume uses a quarter to a third of the capacity. Could have went with a smaller capacity if I knew this but it is nice to only have to charge it on a few occasions.

 

Some pictures

https://share.icloud.com/photos/08cURCLNU04fHPgGD1ehICaxw

[formulaben]

On 4/8/2024 at 11:06 PM, drewsbu said:

...a bit overkill actually.

As I like to say, anything worth doing is worth overdoing.