AGM's will drop to about 13.2v, immediately. This is the float voltage for AGM’s.
Lithium will also drop to 13.2v but maintain that voltage until say 20% capacity remains. This is part of the Lithium chemistry.
In a typical cycle, the AGM’s will be kept at float by the Lithium. So only the Lithium part will be used, but there will still be the AGM that can start to share the load after the Lithium bank has been 80% depleted. So in effect one is cycling only the Lithium part…given that Lithium can be cycled many more times than AGM’s this should be cost effective.
In Practice… imagine 8 AGM batteries of 12v 100AH giving 400AH at 24v. Normally this would be a typical bank. Cycle down to 75% each night. Thus consuming 100A.
Now add two Lithiums of also 100AH 12v giving 100AH at 24v. You now have a 500AH bank….
If you still use 100A then the first 80 will come from the Lithiums or until their voltage drops below 13.2v and then the remaining demand will be supplied from the whole bank. in fact as the lithium voltage drops the AGM’s will take over and start to prop up the Lithiums…so that they do not get depleted too low.
When it comes to charging the Lithiums are more efficient and will accept fast charge, and the AGM’s will trickle full all day if there is sufficient solar….
The end result is that for the cost of only two Lithiums you have in effect a very long lasting bank. The AGM’s only cycle a few percent each day but on occasion they can be as required. They are there as reserve and barely cycle thus will last for a long time maybe more than a decade…
If one was to do this one would have to be very careful connecting the Lithiums… the AGM bank would need to be charged to float 13.2v. The Lithiums would need to be discharged to the same voltage 13.2v so when you connect them together there is no current flow between the batteries. It would be dangerous to connect them with say Lithiums at 13.8v and the AGM’s at 12.5v as it would arc at the moment of contact.
Now shout me down and tell my why this is not a good idea….
Remember the objective is to get the best AH for the lowest cost….
Stored ashore in Leros
On 12 Dec 2021, at 22:17, CW Bill Rouse <brouse@...
Kent, Doesn't this explain the furling and outhaul motors not working properly?
Batteries are like anchors, there are lots of opinions and most opinions are based on limited comparative experience.
This is what I tell my clients and it is totally my opinion:
The best house battery buy is the basic DEKA Marine Master Deep Cycle DC31DT battery which will last 2 years, maybe 3. At $107 each (Lowes in the US) it seems like a bargain regardless of which battery you compare it to. Sure there are better batteries that will last longer, but none will cost you less per month. There are so many disappointments that have been reported by Amel owners, it is hard to choose something else. But when you buy these DEKAs and they fail in 2 years, remember that was the expectation.
And don't forget about the DEKA 12-Volt 1000-Amp Marine Start Battery.
This is what 8 DC31DT batteries and 1 DEKA 12-Volt 1000-Amp Marine Start Battery will cost you at Lowes.
Don't forget to check the water in these batteries. They will not last if you allow them to charge and discharge with low water.
Here I am again, singing the same tune...
In 2018 I bought 8 Crown "deep cycle" group 31s. They were great for about a year, then slowly began to deteriorate. With 520 AHr and fully solar charged by early afternoon, when new I was waking up to 25.4-25.6v after about 50AHr use overnight. This slowly deteriorated until I was running the generator before bed to avoid dropping voltage below 24.7. I nursed them along until July 21 and bought 8 NAPA (Penn)105 AHr group 31s. They have already failed, after working great initially, in just 5 months.
I charge at 28.5v Abs, 27v Float, and equalize at 31v (on recommendation of Crown engineer). I have a 105A Magnum charger/inverter, and 850W solar in 3 pairs, each pair with it's own Victron MPPP controller, and a 60 A alternator using a Balmar external regulator.
My first 3 sets of similar hybrid batteries didn't start to deteriorate until they were 30-36 months old. This started after I installed solar. Watching the voltages and solar output closely shows them acting as they are set to act. Measuring amperage at the primary 25v cable from battery studs to switch, I don't find any excess current flowing with switches on or off. All batteries measure within 0.1v after disconnecting for 6 hours. All cells have SG 1.019 +/- .001, which does not improve after 6 hrs equalizing at 31v. All read within .2v of each other after load testing, which shows them barely in the "fair" range. It doesn't seem to be a matter of one bad battery or cell, or unequal charging...they are all deteriorating at the same rate.
I need new batteries again, and am thinking about AGM golf cart batteries. So far they are all 11.5" height, and my very early SM2000 has only 10.5" battery box height. I'm also only able to install 8+1 group31 batteries, limiting my total AHr capacity.
I'd like to make the switch to LiFePO4, but insurance is proving to be a problem. I had hoped by the time my current batteries failed I'd be able to find insurance...alas, they've gone belly up after only a few months.
I'd love to hear any thoughts about my current ( no pun intended) problem, 6v AGMs that will fit my space, Lithium conversion insurance availability (I'm US flagged, but could register elsewhere, I guess).
Kent & Iris