How can I extend the life of my old lead acid battery bank?

[BjornM]

I have a 8 x 12V 100 Ah battery bank in 2s4p 24V configuration for my off-grid solar powered home. They are of type Sealed Maintenance-Free.

Worked well for 8+ years, and I guess they are pretty much worn out. One of the pairs started getting hot while charging, so I turned off the system and measured the voltages. 14.06V / 9.45V for that pair. The other pairs were at 13.39V / 13.20V, 13.13V / 13.48V, and 14.44V / 12.16V. Those three pairs were still connected together when I measured. The hot pair is now disconnected.

Is there a way to squeeze a few more months out of the other three pairs before I get a LiFePO4 solution in place? Would rebalancing help at this late stage? Take the bank apart, charge each battery individually to 100% and then put the bank back together.

 

[Hedges]

Yes, the batteries getting hot were being over-charged in series with batteries that were under-charged.

Fully charge all batteries individually.
Try to use in series batteries of similar capacity.

"Sealed Maintenance-Free" - does that mean FLA with perhaps catalytic recombination? Or is it actually AGM or Gel?
Many automotive batteries are "Sealed Maintenance-Free" but really FLA. You may be able to pop the caps and add distilled water to proper level.

Charging individual 12V batteries still leaves cells imbalanced. An equalizing charge may help. Even AGM which you aren't supposed to equalize. Following SunXtender's instructions I've done so and got somewhat higher resting voltage, not sure how much capacity if any I achieved.

Prompt full charge after discharge and temperature compensated voltage should help prevent lead-acid from deteriorating as fast.

Open link to .pdf technical manual.

Sun Xtender Solar Batteries - Photovoltaic Battery

The Sun Xtender Battery line consists of specialty lead-acid solar, photovoltaic batteries, and renewable energy storage batteries manufactured by Concorde Battery Corporation.

sunxtender.com

 

[KITROBASKIN]

Not an expert here, but find out which batteries are shot, then exclude them from the bank. Adjust your usage accordingly.

8 years is quite good. You must have treated them fairly well. Do not expect the remaining batteries to last very much longer.

 

[KITROBASKIN]

Next stop. Recycler

 

[BjornM]

Yes, the batteries getting hot were being over-charged in series with batteries that were under-charged.

Fully charge all batteries individually.
Try to use in series batteries of similar capacity.

"Sealed Maintenance-Free" - does that mean FLA with perhaps catalytic recombination? Or is it actually AGM or Gel?
Many automotive batteries are "Sealed Maintenance-Free" but really FLA. You may be able to pop the caps and add distilled water to proper level.

Charging individual 12V batteries still leaves cells imbalanced. An equalizing charge may help. Even AGM which you aren't supposed to equalize. Following SunXtender's instructions I've done so and got somewhat higher resting voltage, not sure how much capacity if any I achieved.

Prompt full charge after discharge and temperature compensated voltage should help prevent lead-acid from deteriorating as fast.

Open link to .pdf technical manual.

Sun Xtender Solar Batteries - Photovoltaic Battery

The Sun Xtender Battery line consists of specialty lead-acid solar, photovoltaic batteries, and renewable energy storage batteries manufactured by Concorde Battery Corporation.

sunxtender.com

Thanks, very helpful.

Most likely AGM, because the separator is "FLEECE Enveloping", which I assume is a type of glass mat. Manufactured as OEM for a store chain here in Sweden. More details here:

https://docs.biltema.com/v2/documents/file/sv/7679120a-cafe-4b98-accf-aedeafb1cc66

I don't have a tool to measure battery capacity. But I could wing it and charge to 100%, then measure the voltage after discharge through a power resistor for a specific time, so I can match up the new pairs.

I've been equalizing them every other month since I got them (built-in function in the charger). The store said it would be fine.

My charger is temp compensated (Morningstar TS-MPPT-60 150V), and I very rarely discharge below 80% SOC (just using 20% of their capacity to prolong life).

 

[KITROBASKIN]

Morningstar, the SCC of champions! How old is it?

 

[Hedges]

I've been equalizing them every other month since I got them (built-in function in the charger). The store said it would be fine.

To what voltage, and for how long?
Normally AGM is not equalized because that can cause loss of water, which can't be replaced.
But if you've done it 48 times in the life of the batteries, must not have been too harsh.
Consider a more aggressive equalization for the ones that are low, if after individual charge and settling for several hours they remain lower than the rest. If after equalization they remain too low, leave out of the bank as Kitrobaskin says.

With the automotive + screw terminals they look like our typical "Marine deep cycle" but labeled for solar. Maybe they are true deep cycle.

How does LiFePO4 price compare to AGM or FLA in your area? 8 years suggests you have not been cycling terribly deep. I'm wondering if lead-acid is a good fit for you. Doesn't have the same temperature issues, and best qualify FLA can last 20 years. AGM I have are rated 10 years.

 

[yodamota]

would you mind sharing your charge settings for the batteries?

 

[KITROBASKIN]

I realize you were not asking me but this is what I got from Interstate batteries a couple years ago. Note the equalization settings. I was planning on doing an equalization quarterly but like so many things, that crazy dream just kind of came and went.

 

[BjornM]

Morningstar, the SCC of champions! How old is it?

Not sure. Bought it 8 years ago second hand. Just had a look at it but doesn't say mfg year. Solid as a rock, never give me problems.

 

[BjornM]

To what voltage, and for how long?
Normally AGM is not equalized because that can cause loss of water, which can't be replaced.
But if you've done it 48 times in the life of the batteries, must not have been too harsh.
Consider a more aggressive equalization for the ones that are low, if after individual charge and settling for several hours they remain lower than the rest. If after equalization they remain too low, leave out of the bank as Kitrobaskin says.

With the automotive + screw terminals they look like our typical "Marine deep cycle" but labeled for solar. Maybe they are true deep cycle.

How does LiFePO4 price compare to AGM or FLA in your area? 8 years suggests you have not been cycling terribly deep. I'm wondering if lead-acid is a good fit for you. Doesn't have the same temperature issues, and best qualify FLA can last 20 years. AGM I have are rated 10 years.

Here is my charging profile:
- Absorption 30.79 V, absorption time 2h30m
- Float 27V
- Equalization: 31.81V for 1h once every two months.

Before I looked at LiFePO4, I thought I would just replace my olds lead acid with the exact same model, they're $178/pc. So for 10 kWh capacity that's $1424. The equivalent LiFePO4 from LiTime (their German store) would be $2120. So then it would be a question of longevity and cycle depth. With the lead acid I went to 80% SOC, with the LiFePO4 I think I can go to 40% and still have more cycles than the lead acid. So lead acid doesn't make sense anymore.

 

[yodamota]

wow that absorption voltage seems high. is that at 25*C? or is that what it is doing now?

 

[Hedges]

That is high - compare to 28.8V on page 19 of the SunXtender technical manual I linked.

Also above Trojan FLA absorption. But the equalization quoted is close to Trojan's equalization.

 

[BjornM]

That is high - compare to 28.8V on page 19 of the SunXtender technical manual I linked.

Also above Trojan FLA absorption. But the equalization quoted is close to Trojan's equalization.

I agree. That's the numbers I got from the seller. But I should probably have used lower voltages and they might have lasted longer. 8 years feels pretty ok though.

My numbers are at 25C, then you've got temp compensation on top of that, but my batteries are always at 22-25C.

Right now it is just end of life management, as I'm getting ready to order LiFePO4 to replace them.

 

[SamDeleted]

8 years feels pretty ok though

8 years is GOOD, you have done well with them

 

[SamDeleted]

Like others have said, chances are most of the batteries are still fine , it's just a few that are starting to die

You could discard the bad batteries , keep the good

that will give you reduced capacity , but I would make up for that with deeper cycles, obviously you'd bit hitting the remaining batteries harder than normal but I think after 8 years it's all a bonus .

Ride them like you stole them until you eventually have to replace , might get another couple of years out of them !

 

[BjornM]

Like others have said, chances are most of the batteries are still fine , it's just a few that are starting to die

You could discard the bad batteries , keep the good

that will give you reduced capacity , but I would make up for that with deeper cycles, obviously you'd bit hitting the remaining batteries harder than normal but I think after 8 years it's all a bonus .

Ride them like you stole them until you eventually have to replace , might get another couple of years out of them !

Thanks buddy, makes sense. But the mental stress level over a soon failing battery system in the middle of winter is eating at me though. I have no grid connection, only rely on solar. Got a petrol generator though. Will be ordering LiFePO4 soon, but takes 2 months from China.

 

[SamDeleted]

Thanks buddy, makes sense. But the mental stress level over a soon failing battery system in the middle of winter is eating at me though. I have no grid connection, only rely on solar. Got a petrol generator though. Will be ordering LiFePO4 soon, but takes 2 months from China.

Yes I understand!

What is the shelf life like on those LiFePo4? I think they can last a good long time in storage?



Not sure how long until winter in Scandinavia (soon I imagine?) don't forget a DIY lithium build can take time and have pit falls , they are great. , but might take a bit of work to get it working!

 

[BjornM]

Yes I understand!

What is the shelf life like on those LiFePo4? I think they can last a good long time in storage?



Not sure how long until winter in Scandinavia (soon I imagine?) don't forget a DIY lithium build can take time and have pit falls , they are great. , but might take a bit of work to get it working!

Not sure about shelf life. Some think that you will never hit max cycle count on a solar power system (one cycle per day), but instead hit number of years life span first.

Yea it looks like I have some learning to do. But I have an electronics engineering background, so I will at least avoid the most obvious mistakes.

 

[KITROBASKIN]

Given the critical nature of your energy use, seems like getting complete batteries with a warranty surpasses going the battery building method. Unless you look at it as a learning experience and a fun challenge. Being able to repair your future batteries I think we can agree is a good thing, though. Keep us informed!