Battery replacement

[gs555]

I’m replacing my house batteries, they are the standard 2 4D batteries used for starter and house. My boat is never connected to shore power and I have a solar system that charges the batteries. I try to run the engine as little as possible. I also have a backup battery jump started just in case.

I’m wondering if I could maybe replace one of the lead acid batteries and then get a lithium battery as my second battery. I know they can’t be connected so one would start the engine and could be charged from the alternator. The second would be house only. The advantage in my mind is that I would have a lot more house battery amperage this way. The solar system can charge two battery banks so that seems like it would work.

Can this work? I’m guessing that for air circulation of the lithium battery I might need to find a different location for it. Anything else I’m missing?

Thanks
Geoff

[wolfe10]

While you could do that, lead acid batteries and Li batteries prefer different charge profiles.

If you combine the two 4D into one bank and the Li into another bank with a different charger that could work. Would still have to limit charge amps to the Li bank from the alternator to prevent the alternator from overheating.

[yodagwb]

your 2 4Ds give you 200ah usable. they can be replaced with a single 200ah lithium, size close to a single 4D. This acts as the house battery and gives you 200AH. Then you get a sealed battery as a started battery which charges off the alternator. If you want to charge the house while motoring, you will need to install a 30amp dc-dc charger.

[yodagwb]

PS- you will have to install a new shore charger as the one currently on the boat most likely doesn't handle lithium batteries.
I made the switch years ago. Best thing I ever did. Refer loves it.

[Triumph]

A long time ago I replaced my lead acid Trojans with AGM batteries. They are 6 volt in series and then parallel. I get 450 amp hours out of this.

Here's the deal : you can find 1-2 year old AGM batteries used, for about $100 each. These are $500 batteries!! Go on Facebook marketplace or CraigsList and you'll see them. What's going on is that a lot of folks with AGM's are switching to Lithium and looking to get rid of the used AGMs. I recently bought 4 - $500 batteries that were in a home solar system. They were 1 year old. I paid $150 each for the 4. Great batteries, lots of AMPs, quicker charge acceptance than Lead acid - no complicated system, keep everything you have and let your solar panels give you all the juice you probably need.

Bill on TRIUMPH in Tampa

[elk]

I have a question. When using a dc to dc converter, do we use isolated or non isolated ground type?
Amazon has 100 AMp AGM Renogy for around $170. Can supply 1100 amps starting current.

Ed

[Olivia Mae]

What you're thinking of could work,but all your charging sources should go to one bank this would be the lead acid one, then use a dc to dc charger to charger to charge the lithium. Not ideal and use of a lithium bank. Really, it would make more sense to do it all in lithium, and upgrade alternator and charging cables to charge it. You could also do something with a dc to dc charger to keep from frying the existing alternator.

Alternatively, you could stick with lead acid. Do 4x 6v golf cart batts series parallel for 1 big house bank. Use the house bank for everything. Then you can add a small 12v group 24 marine start battery for an emergency start battery on the other bank, only to be used if you ever ran the house bank down. Use a battery combiner/isolator to keep the emergency start battery charged. Run all charging sources to house bank. I've done this on our boat and it works great and gives you about a 430 ah bank, 50% of which is usable. Not as much as you'd get from LiFePO4, but less hassle and expense than doing a lithium bank correctly.

[KenKrawford]

One other thought on lithium batteries. Before you go down that road, give your insurance company a call and see if special endorsements are required when you have lithium batteries. I'm not sure all do but it's worth checking.

[elk]

I presently have 4 six volt golf cart batteries in series parallel. Solar at 200 watts, upgrading to 400 watts. Installed a Victron solar controller MPPT 100/30.
Going to replace the batteries with a 100 amp AGM for starting and a 300 amp LiFePo for the house. I plan on protecting the alternator with a dc to dc charger which will also charge the batteries.
My question is: do I use an isolated or non-isolated dc to dc charger?
Any thoughts on this setup will be appreciated.

Thanks,

Ed

[smcgauvran]

Hi Ed,

I made similar upgrades last year. To avoid any issues with the alternator diodes, I ran new lines (pos and neg)from the Balmar alternator to the starter battery. I used an isolated DC to DC charger to avoid adding "noise" to the boat's existing ground system. Wasn't sure if it was necessary, but I wanted to do the task once! I added a temp sensor on the alternator to the external regulator as the LiPo takes a charge more quickly and the demand can cause the alternator to overheat.

The solar charger is wired directly to House battery. The LiPo upgrade was worth it! It's nice to be able to run the A/C for a few hours on the hook to cool the boat down at night without the noise of a genset.

Mike M