LiFePO4 vs FLA - The Real Deal

[ramblinrod]

Hi All,

I have a fair bit of experience with FLA batteries and am trying to figure out what all the hype is about over LiFePO4.

What I have heard so far about LiFePO4 is:

Pros:

Higher energy density. How much? For a given dimension of battery case, lets say equal to a FLA Grp 27 100 A-hr battery, how many more A-hrs capacity does a LiFePO4 have?

Higher Usable Capacity. I hear people tout 80% (charge cycle from 90 - 10%).

Wait a mintute!

Shouldn't we design for 50% reserve capacity?

What if there is no sun or wind one day?

What if the girlfriends hair gets longer and she needs to run the blow drier another 5 minutes per day?

So if we design for 50% reserve capacity of 80% max capacity (so we don't hurt the battery), we're talking cycling the battery from 90-50%.

Wait a minute!

We were cycling our FLAs from 100-50%, and if on occasion we had to dip into the reserve, say to 20%, no biggy as long as we charged right back up again.

We could have design for 100% - 20% charge cycle on our FLAs too. They probably wouldn't last as long, but isn't that a fair weight/capacity trade-off?

Faster Charging: Sure, pound the Amps into that puppy.

Wait a minute!

Where are they going to come from?

The 400W wind genny and the 400 W solar panels will only deliver a high of about 30 A max.

So we are going to be forced to run ICE (Internal Combustion Engine) to gain any benefit of the fast charging capability.

Isn't the goal for most cruisers to avoid running the ICE when it isn't necessary?

Reduced Voltage Sag.

The output remains constant right down to 10% DOD.

Wait a minute!

Voltage sag is never really a problem when using a properly sized FLA bank.

So it seems the only time LifePO4 would really be a benefit if one is going to throw on a thruster, windlass, or huge inverter with heavy load, when the FLA bank is really low.

Is that the only real benefit?

CONS:

Expensive. By the time the batteries are purchased, higher output shore power and ICE charging is included. This "upgrade" will be many thousands of dollars.

Wait a minute!

Wouldn't it be a lot more economical to just use a smaller bank of FLAs with design charge cycle of 100-20%, and replace them more often?

Limited Availability. There are only a few suppliers with limited distribution channels with very limited (if any) stock at the retail level.

Wait a minute!

One can get a replacement FLA battery anywhere.

Consequence of Failure:

If something goes wrong, like the batteries get trashed by an incorrect charge or discharge incident, how much will it cost and how long will it take?

OK, I think that about sums up my thoughts.

To me, the only real benefit I see to switching from FLA to LifePO4 is the ability to say, "I have LiFePO4s".

Am I missing something?