Methods used to recover lead carbon batteries

In my 48v stand alone (off-grid) system I have a battery storage bank, 2 years old, (x 8 Narada Rex Series 6v)
I’ve been told the batteries can be taken away and charged by a specialist charger to recover the storage capacity. I run a back up generator frequently as the battery low capacity indicator initiates at 46.5v which usually happens as soon as the PV array losses sunlight. I was not supplied with an operation manual when my stand alone system was installed so I don’t know the operating parameters and if the battery bank is failing?

Hi Tracy,

Narada Rex lead-carbon batteries generally have a good reputation and should last 5 to 8 years without too many issues. Your system does not sound like it has been designed or setup correctly. Recharging the batteries from a backup generator should occur at around 48 volts, 46.5v is very low unless you have very high loads?

What is the Ah rating of the batteries? Are they getting fully charged at least once a week? If the solar is inadequate and the generator is not charging close to 100% then the batteries may have degraded.

Sometimes you can revive lead-acid or lead-carbon batteries with a very long slow recharge up to the adsorption voltage until the current has reduced to a trickle (less than 1 or 2 amps). What brand inverter and charger are you using?

Thanks for your response and questions. The system comprises x 9 300 DuoMax PV panels, x 8 300Ahr x 6V batteries , 5kw, 48V Integrated Inverter with 80A MPPT, Honda EU301S Inverter Generator.

Loading is pretty light: water pump (with soft start), washing machine cold water only, fridge freezer, gas califont (pilot light), lighting is all LED. The property is a two bed cottage, all the household appliances are switched off when I leave on Mondays and back on on Thursday evening when I return - I do not live there during the week as I work and stay in Wellington City Monday to Thursday. I have a separate diesel generator for powered tools such as my drop saw, thicknesser and compressor.
I leave the power supply to the PV array on constantly.

The system supplier did not give any guidance about needing weekly top up charging, and a connection from the generator to the system was not installed until 20 months after the initial system installation and commissioning. The batteries were also purchased 10 months prior to installation.

The cottage location does not get mobile coverage and I have not yet invested in a satellite link.

Thanks again

I neglected to respond to the inverter question, the unit is not branded so I don’t actually know. I’ve search online and matched the exterior to this

Sorry to break the news but those Voltronic inverters are not very reliable and are difficult to set up correctly. They also don’t have battery SOC (state of charge) controls so I’m not surprised you are having issues. You really need to upgrade to something more reliable such as a Victron Multiplus inverter and solar charge controller (MPPT) which will be able to charge a battery system correctly.

Unfortunately, your batteries may have been in a low state of charge for too long and may not recover. Can you get the battery charge voltage up to 56V for several hours using the generator?

Where are you located exactly?

Hi Jason,

I have not been brave enough to push the battery charge up past 53v because I didn’t know if doing that would cause damage to the batteries or not.

I live in NZ in the Wairarapa.

I am guessing without having a technician actually assess the system that it was not set up correctly. Solar systems in NZ are not as common as in Australia. Technical expertise is not as common either I gather.

I am reaching out to the NZ Sustainable Energy Association for advice.


That’s strange, why were you concerned about going over 53 volts?

The charging (cycle) voltage is 55.2V (absorption) for these batteries as shown on the battery specifications. And 54V is the float voltage (2.25 x 24 cells in total).

If you never charged above 53 voltages then the batteries have never been charged correctly and unfortunately, this is why they have failed.

Yes I understand now the reasons why the batteries have likely failed. The company who supplied and installed my system did not provide any operating instructions. I spent 11 months requesting an operation manual, which I have never received. I had no idea during that time the ongoing undercharging of the batteries was going to cause them to fail.

It does look like I will need to replace the batteries but wanted to find out if they could be rejuvenated through specialist charging.

You will need to try charging them at 55.2 Volts for 2 to 3 hours using a generator or solar. This is the only way to see if you can save the batteries. However, if the temperature in the battery room/box is very warm (above 35 degrees C) then you will need to charge them at a lower voltage (around 54.6V)

Temperatures here are between 8 - 16 degrees C at the moment so no risk of 35 degrees. When you say charging them at 55.2v do you mean get them up to 55.2 v then hold them at that point for 2-3 hours using the generator?
My generator out put

@Tracy, the charger (inverter) will hold the charge voltage at 55.2V but you have to program it correctly. The generator is just the AC power source.

Do you have the inverter manual? You need to change settings 26 and 27. Set the Bulk charge voltage to 55.2V and the float voltage to 54V

If you don’t have the manual, type this into Google and download the PDF file… “Axpert 5kva inverter manual”

@Tracy How did you go? Were you able to program the inverter correctly?

Hi Jason

I’ve not tried yet. I was using my generator all weekend to build my kitchen and laundry cabinets so was not keen to put to much demand on the generator. I’ll try this coming weekend and let you know how I get . Thanks for filling up.