Thread: LiFePO4 or Lead Crystal to replace AGM?

Originally Posted by Milton477

Thanks guys for the replies.
Drivesafe, I was rather hoping you would reply but my biggest question is still unanswered.

If a Lithium battery maintains it's voltage above 12V for the majority vast of the time while being discharged, what does a Lead Crystal do? I can't seem to find a discharge Voltage curve for Lead Crystal. I am interested in comparing the capacities of batteries while their voltage is above 12V.

Hi again Milton, and Lead Crystal batteries have a very similar discharge voltage curve to lead acid batteries.


I am curious as to why this matters?

Thanks Drivesafe,

I'm just trying to compare like for like. Lithium prices for a DIY system are not so far away from Lead Crystal prices as to remove Lithium from consideration. $1200 ish vs $1500 ish for 200Ah. Big weight savings, constant voltage....

Originally Posted by Homestar

I'd like to see that happen too but it seems they are only mining just enough Lithium to meet demand - I think in a deliberate attempt to keep price up. We need to open a Lithium mine and flood the market with cheap Lithium.

There are several already. Just up the road from where I work is Galaxy, Mt Catlin Lithium. I am going to MRL's Tantalum/Lithium mine and there is at least another 1 in WA with prospects of another 2 or 3 coming on line soon. Does not mean the price will reduce drastically as being used in more and more battery applications.

Originally Posted by Milton477

Thanks Drivesafe,

I'm just trying to compare like for like. Lithium prices for a DIY system are not so far away from Lead Crystal prices as to remove Lithium from consideration. $1200 ish vs $1500 ish for 200Ah. Big weight savings, constant voltage....

Hi again Milton, and why the requirement for constant voltage?

Yes, by far the biggest advantage of a Lithium is the weight saving. It's the only reason I'm looking at them. Although my van isn't overweight, it gets very close at times. Going from 2 x AGM's to a single Lithium would save me 45Kg's - a massive difference. Constant voltage isn't an issue - everything you'll run from a 12 volt system copes easily with what a lead acid does as it discharges. If you're getting them down far enough to be an issue - under 12 volts IMO, then you're not doing your battery any favours and reducing their life dramatically.

The cycle life of a Lithium is also very good and makes it quite a good proposition although I've yet to see a Lithium do many years of use yet, so I'm still not 100% sure they'll meet the claims there.

Originally Posted by drivesafe

Hi again Milton, and why the requirement for constant voltage?

Thanks Drivesafe.

Right now I have a pair of 120aH AGMs sitting on 12.3v with no load. Turn on some lighting & the voltage drops to 12v & then the fridge kicks in (140l Waco), or tries to. Voltage drops to sub 11.5v & the fridge turns off. Voltage recovers & the fridge tries again with the same result.

I know or realise now that the cable to the fridge is too small at 2.5 mmsq so this exacerbates the problem somewhat. My research shows Lithiums have a flat discharge curve which drops off only when they are near discharged. I believe that my current problem would not be happening if the voltage remained above 12v. Sure, I am going to upgrade the fridge cable to 6 mmsq based on what I have learned now.

I know that there are a million ways to shoot me down with my problem but I believe that a more constant voltage above 12v is better for 12v devices than 11.8v for example. I know that my caravan air suspension compressor does. Not sure how the modem & CellFi hot spot feel about sub 12v. Also, as the voltage drops, the current rises & stresses small cables & less than perfect connections as demonstrated by my fridge.

If I have to spend the money, then how should I spend it to get the best bang for buck? All features need to be considered.

Hi again Milton, and that is one hell of a voltage drop.


With a pair of 120Ah batteries sitting at 12.3v, unless your fridge is a 3 way, then yes the cable is to thin but a 3 way fridge should never be run off the house batteries anyway.


So I am ASSUMING that your fridge is a compressor type. If so, then just how long is the 2.5mm cable run between the batteries and the fridge because, even with 2.5mm2 cable, you should not be seeing anywhere near that sort of voltage drop.


Can you post up some more details because under normal operation, with 2 x 120Ah of house battery capacity, even with a few lights running, your fridge should not pull the batteries down more than 0.2v, but 0.1v would be expected.


Something seems to be wrong with your setup and fitting any type of new batteries may not fix anything.

BTW Milton, not intearested in “shooting you down”, more interested in trying to help you, which ever way you choose to go.

Originally Posted by Milton477

Right now I have a pair of 120aH AGMs sitting on 12.3v with no load.

AGMs sitting with no load should be 13.1 volts so as you mentioned your batteries are very tired. (I run a bank of 6x140ah Century AGMs)
80 amps drawn from a small bank of batteries < 200 ah will always see some serious voltage drop although I understand lithium do better.