Increase the capacity on Lead Acid batteries

[kje]

Hi, I have a few Lead Acid 55Ah 12V batteries holding it's voltage at 12.7V, but I've measured the capacity to about 20Ah. Is there a way to increase the capacity on these batteries?

 

[amberwolf]

12.7v is nowhere near charged up. 14.4v is closer to normal full for an SLA battery. FLA are a little different but close enough.

As for capacity, what rate did you drain them at to reach the 20Ah? Most of these are only capable of their rated Ah at 1/20C drain, which means for a 55Ah 55/20=2.75A max. Higher than that and you get less, much higher and it's usually a lot less. Look up Peukert Effect.

Plus, if they are only reaching 12.7V and/or only being charged to that in the first place, you can't get their rated capacity cuz they're simply not fully charged yet.

 

[999zip999]

Lead. Look up desufation or pulse charging of different sla batteries.

 

[kje]

Resting voltage is 12.7

The discharge rate I used was 1A with my Imax B6 Multifunction Charger. The display showed mostly 0.5A during discharge.

I stopped discharging at about 10.8V. After sitting a few hours the rest voltage was 12.0V exactly.

The discharge test took about two days. I don't know the battery age.

Two of them are maintenance-free batteries, is it impossible to open them up? I can't see the filler caps... One of the batteries had filler caps and I measured between 1250 and 1260 with my acidmeter.

 

[Punx0r]

Lead acid is fully charged at 12.65V and discharged at 11.8V. Resting voltages, obviously. Since you stopped at 12.0V you probably left about 20% capacity in there.

 

[bikeelectric]

Resting voltage is 12.7

The discharge rate I used was 1A with my Imax B6 Multifunction Charger. The display showed mostly 0.5A during discharge.

I stopped discharging at about 10.8V. After sitting a few hours the rest voltage was 12.0V exactly.

The discharge test took about two days. I don't know the battery age.

Two of them are maintenance-free batteries, is it impossible to open them up? I can't see the filler caps... One of the batteries had filler caps and I measured between 1250 and 1260 with my acidmeter.

You didn't say what the capacity of the batteries are or what the voltage of the pack you are using . Are you using three batteries in series for 36v ? Those sealed AGM ( or gell but you probably have AGM ) batteries are good for about 5 years or less and then they loose quite a bit of capacity. An AGM battery will not cycle as many times as a good quality deep cycle flooded lead acid battery ( the kind you can check the electrolyte on).

The flooded battery you can do an equalize charge to ensure that all the cells are balanced What happens with lead acid batteries is that one cell will get weak and continually gets weaker. The equalize charge is a controlled overcharge - up to 15 volts for an hour or two. You can't do that with the sealed AGM batteries because they will vent and also there is no way to top off the electrolyte with distilled water like with the flooded battery.

So my guess is that if your AGM batteries are old ( look for a date code on it ) then they are at the end of their useful life unless you have a use for them that does nt require a lot of current or capacity. The flooded cell may last longer than 5 years but with all lead acid batteries their self discharge rate goes up over time - meaning it won't store for as long. Basically age is determining factor along with the number of times it has been discharged - more deep discharge means less cycles per lifetime. Best is to not take them down more than 50 percent and most of the ratings given are for 80 percent .

Also it is not good practice to use lead acid batteries of different age together .

 

[amberwolf]

You didn't say what the capacity of the batteries are

You might check the first post in the thread for that.

 

[kje]

You didn't say what the capacity of the batteries are or what the voltage of the pack you are using . Are you using three batteries in series for 36v ? Those sealed AGM ( or gell but you probably have AGM ) batteries are good for about 5 years or less and then they loose quite a bit of capacity. An AGM battery will not cycle as many times as a good quality deep cycle flooded lead acid battery ( the kind you can check the electrolyte on).

It's 55Ah 12V batteries used separate. They are flooded lead acid batteries.

The flooded battery you can do an equalize charge to ensure that all the cells are balanced What happens with lead acid batteries is that one cell will get weak and continually gets weaker. The equalize charge is a controlled overcharge - up to 15 volts for an hour or two. You can't do that with the sealed AGM batteries because they will vent and also there is no way to top off the electrolyte with distilled water like with the flooded battery.

I did an equalize charge on one of the batteries now for 4 hours with 15.2V from a power supply. I measured about 2A going into the battery.

I'm excited about a new capacity measurement after resting.