Battery replacement

[killsumptin]

After checking my batteries with a hydrometer after fully charging, I noticed some had 100% charge and some had 75% charge.

I know that you aren't supposed to mix old and new batteries , but could I replace the 75% charge batterys first , without harming the new batteries?

I want to add 2 additional 6v batteries to go to 48v anyway, will 2 new batteries added to the old pack be a no no?

I know that I really need 8 new 6v batteries but my wife and my budget would be happier if I bought them 2 at a time.

[Nate]

You caught your batteries in an unbalanced state, good catch!

Take a 6V manual charger and bring the low batteries up. How long? Until they read full or the battery case starts to feel warm.

[killsumptin]

If I don't have a 6v charger can I isolate the batteries and charge two at a time wired in series?

[Nate]

Yes but pay attention to temperature of the batteries. If one reaches full charge first it will have to stay on the charger until the other reaches full. An overcharge also balances the cells and is good to do once in a while.