Do AGMs have more usable capacity than regular Flooded?

[newhaul]

Originally Posted by Adelie

Actually the power density for lithium is similar to LA batteries. It's the specific energy (energy per weight) that is much better.

Sorry but i disagree my 250ah lfp takes up about the same space as a single T105 6v
So i can have double the power in the same space as a pair of them . All at 12v nom.

[Adelie]

Originally Posted by newhaul

Sorry but i disagree my 250ah lfp takes up about the same space as a single T105 6v
So i can have double the power in the same space as a pair of them . All at 12v nom.

Right now Battleborn seems to be the industry leader for retail LiFePo 12v plug and play batteries.
100Ahr, 17.6lb
12.75 X 6.875 X 9 in. (L x W x H) = 789ci.
1.52Whr/ci, 68.2Whr/lb
https://battlebornbatteries.com/prod...cycle-battery/


Firefly
116Ahr, 76lb
(L x H x W) 13.4" x 9.4" x 6.8" (340 x 238 x 172mm) = 857ci
1.62Whr/ci, 18.3Whr/lb.
https://www.emarineinc.com/Firefly-O...oup-31-Battery

For DIY installations the numbers may be somewhat different. For an apples to apples comparison volume and weight of the BMS and wiring and wasted space between cylindrical cells need to be included in the LiFePo values. Using prismatic cells the energy density is probably somewhat better even counting the BMS but it is not going to be even twice as good.

[Pegu Club]

Our two Firefly carbon foam AGMs at 116 amp hours each can be drawn down eighty percent and charged back up repeatedly, although we have had no need to draw them down that far as of yet.

We are full time cruisers in our third year, we charge our Fireflies with two one hundred watt Renogy flexible solar panels each with their own controller, and the 75 amp alternator on our Beta 16 diesel, The draw down capacity is why we purchased them, kind of the poor mans Lithium batteries so to speak.

Fair winds,

[newhaul]

Originally Posted by Adelie

Right now Battleborn seems to be the industry leader for retail LiFePo 12v plug and play batteries.
100Ahr, 17.6lb
12.75 X 6.875 X 9 in. (L x W x H) = 789ci.
1.52Whr/ci, 68.2Whr/lb
https://battlebornbatteries.com/prod...cycle-battery/


Firefly
116Ahr, 76lb
(L x H x W) 13.4" x 9.4" x 6.8" (340 x 238 x 172mm) = 857ci
1.62Whr/ci, 18.3Whr/lb.
https://www.emarineinc.com/Firefly-O...oup-31-Battery

For DIY installations the numbers may be somewhat different. For an apples to apples comparison volume and weight of the BMS and wiring and wasted space between cylindrical cells need to be included in the LiFePo values. Using prismatic cells the energy density is probably somewhat better even counting the BMS but it is not going to be even twice as good.

The real problem is that the battleborn and other drop in lfp replacements cases are built to fit a lead battery form factor .so the cases are filled with needless foam and other fillers. That is one of the advantages of diy systems . Then there is the price part . My system all in was right at 600 USD including new battery monitor.

Edit my bank is 250ah lfp and weight is approx 55 pounds all in

[Adelie]

As I wrote, if you go DIY then you can get somewhat better Energy density rather than slightly worse.

[sailingchiro]

If you are only going for one long trip per year, just run the engine or buy a Honda 2000. Don't worry about power consumption until you need to change to a more longer term solution. Run the diesel for $1/hour and be happy with it. Don't try to re-invent the wheel until you need it. A fuel can of diesel can solve alot of problems.

[sailingchiro]

Adding solar can open a can of worms! I have added a "new house" system with solar and everything involved including Lifepo4 (almost 700 a/h) at 24 volts to run all refrigeration on boat (2 freezers and 2 refrigerators) at a cost of over $3000. Works great and will be used for months off shore power this year. If I were using for a few (2-6) long trips per year, I would run the diesels or genset and forget re-inventing the wheel. Save thousands and put in having fun at destinations. If you need to replace the batteries, get the Duracell or go to golf cart battery place.

[T1 Terry]

Originally Posted by sailingchiro

If you are only going for one long trip per year, just run the engine or buy a Honda 2000. Don't worry about power consumption until you need to change to a more longer term solution. Run the diesel for $1/hour and be happy with it. Don't try to re-invent the wheel until you need it. A fuel can of diesel can solve alot of problems.

Hard to argue with, there is a lot of energy packed into each gallon at a rate far cheaper than battery storage. The generator will provide stable power for as long as it keeps running and the load is not exceeded. Problem is, they don't make silent non vibrating ones so the peace and quite of batteries and solar need to be measured in $$ terms.
If you need 12v from you 12v battery, look at the C rating used to measure the battery capacity. Generally C20 is used for deep cycle, quality batteries use a C10 rating. This is the number of hrs before the battery goes from fully charged to fully drained. Divide the capacity by the C rating and that is how many amps you can draw to get the full capacity.
OK, to hold 12v under load, that number of amps can be drawn for half that time and the battery should still deliver 12v under load.
If you need 100 amps and the batteries are rated at C20, the load capacity for each 100Ah of battery capacity is 5 amps, so 20 x 100Ah capacity would be required if that 100 amp output @ 12v under load was still needed at a 50% SOC.

This is where quality lithium batteries come into there own. That can deliver the 100 amps from a 100Ah battery all the way down to 0% SOC while still under load.

T1 Terry

[StuM]

Originally Posted by T1 Terry

If you need 100 amps and the batteries are rated at C20, the load capacity for each 100Ah of battery capacity is 5 amps, so 20 x 100Ah capacity would be required if that 100 amp output @ 12v under load was still needed at a 50% SOC.

Again, confusion of terms. "load capacity" is measures in Amp hours not Amps.



Are you saying that you need a 2000Ah bank to deliver 5 Amps at 12 Volts when your bank is at 50% SOC?


If so, you have misunderstood what C ratings are all about.


All the C rating tells you is how many usable Amp hours you will get out of a battery at different current rates (i.e. on a steady draw at a certain number of Watts or Amps)



Heck a 70Ah starter battery can give you 100Amps at 50% SOC (admittedly not for long).

[T1 Terry]

Originally Posted by StuM

Again, confusion of terms. "load capacity" is measures in Amp hours not Amps.



Are you saying that you need a 2000Ah bank to deliver 5 Amps at 12 Volts when your bank is at 50% SOC?


If so, you have misunderstood what C ratings are all about.


All the C rating tells you is how many usable Amp hours you will get out of a battery at different current rates (i.e. on a steady draw at a certain number of Watts or Amps)



Heck a 70Ah starter battery can give you 100Amps at 50% SOC (admittedly not for long).

Not load rating, peak load to maintain an expected voltage drop under load. At 50% SOC, if you wanted to draw 100 amps and still maintain 12v while drawing that 100 amps and the 100Ah battery is rated at C20 to get that 100Ah capacity, you would need 20 x 100Ah lead acid batteries, no matter what form of electrolyte stabilising is used, flooded cell, absorbed glass matt or Gel, lead crystal etc
Start batteries are built in a different way to deep cycle batteries because they are designed for a different purpose. Multiple thin plates for a high current discharge battery that doesn't have a lot of AH capacity but can deliver high current for a short term, or thicker plates for batteries designed to store large amounts of energy but available at a much slower rate and charged at a much slower rate.

T1 Terry

[smac999]

the c20 rating has nothing to do with voltage drop under high load. not sure where you came up with that. voltage drop under high load would be a CCA rating.


if a battery has a c20 (hour) rating of 100ah that means you can draw 5a load for 20 hours.

the same battery would likly have a c10 (hour) rating around 90ah so you could pull 9a for 10 hours.

the same battery would likly have a c5 (hour) rating of around 80ah. which means you could pull 16a for 5h.

pulling 100a from a 50% SOC battery would definatly have different voltages results from lead vrs agm vrs brand vrs quality vrs age. all of them could have the same c20 rating for slow discharge.

a 50% battery is already at 12.0v so any load will drop it under 12v. good thing starters, windlasses etc all work at ~9v.

[sailatkin]

Great discussion on AGMs etc. I have Mastervolt AGMs on my boat - two 6V 260 AH house batteries, one 12V 70 AH start battery. Replaced the house batteries after 5 yrs - the engine battery just died after 3.5 yrs. Every week or two I flip on the charger to top them off and I have never run them down. Any thoughts on why they appear to die so fast?

[argonauta1]

My experience with AGMs are they are too susceptible to charging issues which seriously reduce their life. I stick with gels and or flooded.

[dmkkeng]

Originally Posted by George_SD

Stock 20A Xantrex TrueCharge and whatever stock alternator came with the boat.

As as mentioned in my post above - going with anything but FLA at this time is going to be price prohibitive as full upgrade of the charging system would be needed and I don't have the that kind of money for this project at the moment.

I went through the same process 4-5 years ago, I purchased Flooded Cell batteries for economic reasons however the next time I will likely go with AGM batteries for the following reasons;
- increased usable capacity for the same size batteries
- no maintenance required
- no off gassing during the charging process
- quicker recharge time

My only concerns would be cost and the possibility that AGM batteries will not tolerate off grid charging as well as Flooded Cell batteries. I'm not so sure this is true, I had at least one of my flooded cell batteries fail prematurely.

You mention you have a 20 amp charger, the general rule is your charger capacity should be at least 10% of your total battery capacity. Based on this rule your charger will only support a total battery bank capacity of 200 amp hours.

[newhaul]

Side note for everyone in this situation or considering it in the near future .
Lfp prices are falling rapidly
Mind you these numbers are from the ev market but will apply to us similarly
That figure now stands at roughly $137 per kilowatt-hour, and likely to plunge to about $100 per kilowatt-hour in the next couple of years,
It was well over $1100 per kwh 10 years ago.