How to charge dead batteries?

[grhopper]

I have an RXV with a 6x8v setup. The cart got left off the charger for a while, and now the SOC has dropped too low for the stock charger to work (2 red blinks). My SOC meter was reading around 17v.

I have a Stanley Fatmax charger that has a voltage selector for 6, 8, 12, 24, 36, and 48. I've tried connecting it to the full pack and selecting 48, but it doesn't seem to recognize it. I've tried a couple of single batteries set at 8, and the fault LED will blink while the charge LED is lit, but it will go switch to ready after a short period of time.

Is there a way to recharge a battery that is down to 2 or 3 vaults, or did I kill my batteries and need to replace them?

[usgicollector]

Put it on 8v setting and charge one battery at a time for one half hour. When done see if golf cart charger will turn on. If that doesn't work do another round. Do this till the golf cart charger takes over. You don't have to unhook any cables to do this.

[ARKSoft84]

Your going to have to get an old school charger that doesn't have any advanced "smart" features.

[Gregorio]

As a last resort, you might try charging each 8V battery with the charger set on 6V. This will lower the turn on threshold for the charger. If they are still good, the voltage will come up to about 6.2 and then the cart charger might recognize the pack.

But, if you did not destroy them completely, you reduced their life a lot.

[grhopper]

Originally Posted by usgicollector

Put it on 8v setting and charge one battery at a time for one half hour. When done see if golf cart charger will turn on. If that doesn't work do another round. Do this till the golf cart charger takes over. You don't have to unhook any cables to do this.

I can't get it to charge doing a single battery. Can I do 2 batteries at a time set to 8v?

[Sergio]

Plug your multi-voltage charger back on the entire pack and set it for 24v.

Once that is done, leave it connected to the pack and set it to 36v.

Once that is done, leave it connected to the pack and set it for 48v.

You can charge any number of batteries together (Ie: 2 batteries on the 6v or 8v setting) as long as the batteries are not internally shorted.

[Whitaker]

Edited.. Now editing back. With 12v deep cycle batteries like for my camper, if they fall to a low soc a charger will not charge them back. But if you hook a set of jumper cables to it and leave it for a while then it will charge from the charger. Not sure about a 48v system but like Sergio suggested maybe try charging two or three at a time with jumper cables. Somebody block me if it's not recommended. But due to amperage I'm not sure if you will get feedback to the 12v vehicle.

[Sergio]

If Your charger is "too smart" to even try, You can do like Whitaker suggested and connect a 12v jumper to 3 batteries at the time.

Do both halves then connect 2 batteries at the time to the 12v jumper.

That may get them to where the smart charger will work.

Edit:
Remember to always make the last connection on the +12v battery side as there could be a lot of hydrogen gas around the fast charging 8v batteries and you don't want to add a spark.

[radioman]

Originally Posted by Sergio

Plug your multi-voltage charger back on the entire pack and set it for 24v.

Once that is done, leave it connected to the pack and set it to 36v.

Once that is done, leave it connected to the pack and set it for 48v.

You can charge any number of batteries together (Ie: 2 batteries on the 6v or 8v setting) as long as the batteries are not internally shorted.

That is exactly what I would have recommended. OP didn't mention how long batteries had been left off charge but I bet they are sulfated and beyond charge.

[Jaymo]

That is some serious over-discharge.
I hate to be the bearer of bad news, but your best move is to replace the batteries.