Thread: Lead Crystal

Originally Posted by drivesafe

Hi Kidbeen and you don't quite understand the difference in technologies.

If you have a standard 100Ah AGM, then you have a total of 80Ah of usable capacity, based on a C20 rating, because most AGMs can not be discharged below 20% SoC without damaging them.

If you have a 90Ah Lead Crystal battery ( 6-CNFJ-90 ) then based on the same C20 rating and the fact your can safely discharge Lead Crystal batteries down to 0% SoC, you have 100Ah available for use. A 70Ah Lead Crystal battery will give you 78Ah of usable capacity. Near equal to that of a 100Ah AGM.


But a Lead Crystal battery can be smaller for the same amount of energy required ( see above ) and a Lead Crystal battery will out last an AGM by 2 to 3 times.

It all depends on usage, and the more you intend to use a battery, the greater the cost advantage is to use a Lead Crystal Battery over a standard AGM.

Thanks for setting me straight. Electronics are not one of my strengths but I thought I would be polite and reply to his question.

I also heard that lead crystal batteries can now be used full time as starter batteries. Is that factual?

Originally Posted by Kidbeen

I also heard that lead crystal batteries can now be used full time as starter batteries. Is that factual?

Hi again Kidbeen, to my knowledge, they are NOT suitable for use as cranking batteries.

I also do NOT recommend their use in engine bays.

A cranking battery version is on the way, but I do not know when they will be available.

Originally Posted by drivesafe

Hi again Kidbeen, to my knowledge, they are NOT suitable for use as cranking batteries.

I also do NOT recommend their use in engine bays.

A cranking battery version is on the way, but I do not know when they will be available.

Seeing you are the dual battery expert, you will know the answer to this question:-

My starter battery and Lead Crystal battery are connected via a Redarc Smart starter. I have had the batteries fully charged and the red Led was glowing on the Redarc. When I measured both their voltage they were both the same at 12.51V. I have just pulled the following from another forum but it was a 2009 post:-

"Until about 2 yrs ago, the Redarc battery isolators would remain active until the battery voltage dropped to 12.5 volts. More recent models 'turn off' when the battery voltage drops to 12.7 volts. I recently had one custom made & stipulated this cut off be set at 12.9 volts.

The red light will remain on until the battery voltage drops to the cut off level. I found that 12.5 volts was too low if camped in the one spot for around a week. With a start point of 12.5 volts, the battery voltage would drop to about 12v after a week due to the computer type items that keep operating when the vehicle is turned off. Also constant door opening drops the voltage with the internal light going on & off.

The customised Redarc isolator cost $160 in lieu of the normal $100 approx."


What is the science in reducing the voltage to 12.5v rather than 12.7V?

Hi Kidbeen, the lowering of the Cut-Out/Turn-Off voltage is more to do with the Cut-In/Turn-On voltage level.

Before the introduction of variable voltage alternators, or so called "smart alternators", the Cut-In/Turn-On voltage of most isolators was 13.7v or a little higher for some.

These usually had a Cut-Out/Turn-Off voltage of around 12.7 to 12.9v

This was all good and well until alternators would some times drop below 12.7, turning the isolator off, but then not get back up to 13.7v, so the isolator would remain off.

So they dropped the Cut-In/Turn-On to around 13.2v and at first, left the Cut-Out/Turn-Off as was.

In many cases, because the Cut-In and Cut-Out voltages were now to close, this resulted in the isolator oscillating, continually turning on and off all the time you were driving.

This type of isolator oscillation also caused problems in many new vehicles, including Discovery 3s when they first came out.

So they eventually dropped the Cut-Out/Turn-Off voltage to 12.5v and this stopped most of the oscillation.

Fortunately, my isolators have never suffered with this type of problem.

Can I ask how lithium and lead crystal batteries compare? Advantages and disadvantages?
Possible uses would be either as a second battery or in a camper trailer.
I like the idea of getting two smaller batteries into the space needed for a single AGM, plus the weight saving.
I also like the idea of being able to discharge batteries deeper than AGMs.
What do you think?

Originally Posted by drivesafe

Hi Kidbeen, the lowering of the Cut-Out/Turn-Off voltage is more to do with the Cut-In/Turn-On voltage level.

Before the introduction of variable voltage alternators, or so called "smart alternators", the Cut-In/Turn-On voltage of most isolators was 13.7v or a little higher for some.

These usually had a Cut-Out/Turn-Off voltage of around 12.7 to 12.9v

This was all good and well until alternators would some times drop below 12.7, turning the isolator off, but then not get back up to 13.7v, so the isolator would remain off.

So they dropped the Cut-In/Turn-On to around 13.2v and at first, left the Cut-Out/Turn-Off as was.

In many cases, because the Cut-In and Cut-Out voltages were now to close, this resulted in the isolator oscillating, continually turning on and off all the time you were driving.

This type of isolator oscillation also caused problems in many new vehicles, including Discovery 3s when they first came out.

So they eventually dropped the Cut-Out/Turn-Off voltage to 12.5v and this stopped most of the oscillation.

Fortunately, my isolators have never suffered with this type of problem.

Thanks for the explanation. It is so good to understand why the isolator dropped the voltage to 12.51 as I guessed there was some good reason for doing it.