Dual batteries; best to replace both batteries at same time?

[koifish]

Starting battery just died. Is it best to just replace both that and secondary battery at the same time? Starting battery is 4 yrs old, and secondary battery is 2 yrs old fyi. Thanks!

 

[Cruiserdrew]

What kind of dual system do you have? For most, they are completely independent, so no need to replace both.

 

[koifish]

Pretty basic setup. Bluesea 7610 charging relay with 200amp fuses at each battery. Okay thanks, thats what i was thinking. Reading too many threads making me paranoid i guess.

 

[cjmoon]

With a good isolation like blue sea no issue independent. If your running a dual full time life or many diesel trucks. I have always replaced together but they are always let bled via direct cable.

 

[Dave 2000]

Yep, independent use purchase just the one, continuous dual use replace both.

Regards

Dave

 

[mudgudgeon]

Yep, independent use purchase just the one, continuous dual use replace both.

Regards

Dave

Agreed, if you have a good battery isolator system, just replace one.

I've had diesels with dual batteries that are linked permanently, and one bad battery will drag down the other

 

[greentruck]

I'm running gas. I use a standard Interstate battery in the primary tray. In the almost decade we've had the truck (new batteries, a second tray, and a Hellroaring isolator installed right after purchase) we're now on our third primary battery. The truck is mainly used around town except for far too rare road trips, so very hard service on a starting battery. Lots of starts and short trips.

The original Interstate marine/cranking in the auxiliary tray will still run my CPAP all night, but I suspect it should maybe be replaced on age alone sometime in the near future considering it is part of a life-support system. With a good isolator system you should see results like this.

With linked batteries in a 24 V diesel system, for instance, as was noted, best to replace all if normal use/aging is involved. If one battery suffers a case, post, or plate failure and the group is youngish, you can get away with doing a R&R on just the failed one, but the new group will likely not have quite the longevity of the good original group at that point in time.