6V Batterys...Adding 2 new batterys to the existing batterys

[Klaybus]

I've got 2 6 V Interstate batterys that are 18 months old & am considering adding 2 new ones to my RV for a total of 4.
Would adding 2 new batterys to the 18 month old battery be NOT advised or will it be OK? I've heard that adding 2 new to 2 old (18 months) could cause ill effects to the newer pair of betterys. What do you think?

Thanks,
Clay

[Klaybus]

I've got 2 6 V Interstate batterys that are 18 months old & am considering adding 2 new ones to my RV for a total of 4.
Would adding 2 new batterys to the 18 month old battery be NOT advised or will it be OK? I've heard that adding 2 new to 2 old (18 months) could cause ill effects to the newer pair of betterys. What do you think?

Thanks,
Clay

[Rick A]

Just my opinion, I'm sure other may disagree. If the the old batteries are in good condition (have them checked by a good battery dealer), then there should be no problem. I added a second identical battery battery to my trailer a year apart and there was no problems with either battery. I also had to to do the same with my truck, and again no problems. In both cases I had the original batteries check and they were both in excellent condition before adding the new ones. If the old ones are in less than excellent condition, then I would replace all of them.