A cardinal sin???

[hlev00]

Buy some Lithium now along with a DC-DC charger. Move the solar to the Lithium and leave the house loads on the AGMs. Use the DC-DC charger to pump up the AGMs and house loads. What's left in the Lithium and AGMs should carry you through the night. When you are ready to do the real Lithium upgrade the Lithiums and DC-DC can probably be resold if you can't find a use for them in your upgrade.

Of course you need the space and ability to make up the necessary cables to do this.

[aqfishing]

Have you had your batteries load tested? You may have one bad battery pulling the the whole bank down?

[Nicholson58]

Originally Posted by Tortuga's Lie

I think the big thing is the premature death of the new battery, as you already know but how long this will work is a big question mark. How old are your current AGM's? If they are less than 8 years old, there could be something going on that is killing them quicker.
Can you pair down your refrigeration and run on 1 fridge and 1 freezer? This would help the situation but I am sure you've considered this already as well.

We started with Lifelines. Switched to Firefly. 660 Ah at 24 VDC. Fireflys cratered after only three years. Very disappointing.

Putting a new battery in company with failed batteries will destroy the new one.

We switched to Blue Heron LiFePo including the start battery. hank@starboardlanding.com

Hank was extraordinarily helpful in the transition finding links to programming our devices and including patch cords and dongles necessary.

This change is game changing. 710 Ah running at 26.6 to 27 volts. Solar 985 watts MPPT. We are fully charged daily. Our load is around 120 Ah.

Lithium does not taper off at any part of charging until 100%. Occasionally, we pop on the generator maybe two hours per week.

SV Roxy, Currently in Antigua, Faulmouth Harbor

[OS2Dude]

I take it you are not switching to LFP now because of availability? If you can get good ones now, I would not wait. If you can't, then I would do as suggested and remove the worst batteries from your bank, maybe get one or two expendable AGMs.

What else do you have running in the evening/night/early morning? As stated, the refrigerators/freezers should stay cold as long as you don't open them much (at all). If they are running that much at night, they may need attention. Try packing the freezers densely so you have a cold mass. Same for the refrigerators. If you have items you need/REALLY want from the fridge in the evenings/night, keep those in a single unit.

If you have Victron components, I just ordered a new EPOCH 300Ah V2 LFP. There is also a 460Ah version. The V2 means it can be a part of the Victron environment via the BMS.CAN bus on a CERBO.

https://www.epochbatteries.com/colle...rine-batteries

[TBW]

before installing lithium, check with your insurance company

[usamink]

If your starter batteries are not brand new, I would use them as a supplement to your consumer batteries and then buy new starter batteries.
When you switch to lithium, you also have completely new starter batteries

[TPG]

I went LiFePo4 and flat out love it. Ignore the curmudgeons and do your own research, there's lots of great reasons to embrace lithium.

[T. Lee]

Have you checked the freezer insulation for water (condensation)? Can you add more insulation?
I use only Lithium 24v for house and 12v for starting, and the Lithiums are charged from solar, generator or 2nd alt 24v on engines. Lithiums will accept charge at high rates and fast. The 24v alts must have adequate cooling ventilation.

[nofacey]

Get a battery tester - $25
https://www.amazon.com/sspa/click?ie...tdGY%26psc%3D1

Ditch any bad batteries

Eat down 1/2 your frozen/refridgerated food,, and turn off 1/2 the systems. (Unless the issue is beer vs food……that’d be a real conflict….)

[Traumerei]

Just because your batteries draw down at night doesn’t actually mean they’re the problem although they may be damaged and need replacing.

Disconnecting the batteries and doing a load test on them individually will give you a better idea of their state.

Also, in response to someone else you mentioned the number of fridges and freezers you have and they could easily be the source of your issue. Check the sea strainers if they are water cooled. Reduced flow can make the compressors run longer and harder. If you an infrared temp sensor check their temperature. If they’re hot and the stickers/labels on them are deeply discolored from excessive heat, they have issues. If your compressors have cooling fans make sure they’re clean and the compressors have adequate ventilation.

Lithium batteries are awesome but your total power consumption needs to be addressed.

Just out of curiosity, is anyone onboard charging laptops or using electronics at night?

[EmeraldCoastSailor]

I bet it would work. The new battery would be sacrificial but you know that going in. Just depends on how the existing batts pull down the new batt.

[kubota]

buy conventional lead acid cheap, isolate with a couple schottky diodes for $5 apiece off digikey.
diodes will match charging voltages approx also.
hold you over till replacement.

[Andrew Lippman]

I'm not sure what your are trying to fix. Batteries don't generate electricity, they store it. If your net energy needs exceed the capacity of the sources of that energy no amount of battery storage will help. Think of a simple example: an alternator and a battery. All the energy is coming from the alternator. A larger battery allows for more time between running the alternator, but the net alternator time is the same (to a first approximation).

~800Ah is quite a large bank. 2700 watts of solar is also quite large. First, total up your energy consumers, then calculate what the sources will provide, then add batteries to even out the cycles.

[MVDarlin]

I would disconnect and separately load test all batteries. Then try to recondition any weak ones. I have had success with this using a NOCO 10 amp charger. It has a recondition setting that applies high voltage for 4 hrs to desulfate the battery.

I run 4 AGM group 31 for my house / start bank. It is solar fed and runs a refer as well as pumps and lights. I turn off tge refer overnight

I have a sepsrate solar system with a 200ah Lithium battery for my freezer.

[cakesy]

Just switch everything off overnight. The fridge and freezer will be fine. What else are you running? Lights do not need much.