Adding a Third Lithium Battery

[DT6]

Hey All,

I currently have two 100An SOK lithium batteries I purchased almost exactly two years ago. I sent these to SOK about 6 months ago due to some issues and they replaced the BMS on both and returned them. Now SOK has a really good sale going for the same battery at $299. I emailed SOK and they told me it would be fine to add this "in parallel" to my current parallel configuration of two. I'm also assuming the new BMS I received earlier this year is the same on the new ones they sell. I've got the Escape Victron / Lithium setup.

Does anyone disagree with SOK that adding a third battery, even the same model from the same manufacturer, will be fine?

The reason I'm asking is I have some memory of a comment by someone (from this forum I think), mentioning that you really should not mix batteries of different age.

As to why, I just want extra reserve for emergencies as we travel in winter mostly. Thanks!

 

[John in Santa Cruz]

It should be fine. Wire them like this, it equalizes the load to the batteries. If you can, fully charge the new battery before you parallel it with your presumably already fully charged batteries, this way the old batts don't dump massive current into the new one before they equalize.

to fully charge the new battery, plug the trailer into shore power overnight before you disconnect the old batts, then disconnect the old batts and JUST connect the new batt, plug back into shore power overnight, THEN connect all 3 batts as shown above.

oh, all 4 of the battery interconnect wires should ideally be the same gauge and length. I have the crimpers and ring terminals so I can make my own up to about AWG 2, and I even have some red and black #2 gauge cable left over from my big rewiring job. A old school non-big-chain car parts store should have a small selection of battery cables like this, you might have to ask at the parts counter.

 

[alanmalk]

Another option, although with some minor complications: Use an "A"-"B"-"Both" switch like boaters do. This will keep the new battery isolated from the entire trailer circuit unless you need it. This way you can add any size/capacity battery as a backup. Does require extra wiring and some planning, however.

 

[Ron in BC]

Yup, works for me with two different battery types.

Ron

 

[John in Santa Cruz]

I'm not a fan of A/B battery switching...

switching to BOTH after one or the other is partially discharged is bad news, the fully charged battery will RAM current into the other batteries, easily 100A or more... and only the 'active' battery is getting charged. I would want a shunt monitor on EACH side of that, so two battery state displays.

 

[alanmalk]

On a boat, "Both" is used when the situation is truly desperate and the lifespan of the batteries doesn't matter a hoot.

 

[GinoandLinda]

I'm not a fan of A/B battery switching...

switching to BOTH after one or the other is partially discharged is bad news, the fully charged battery will RAM current into the other batteries, easily 100A or more... and only the 'active' battery is getting charged. I would want a shunt monitor on EACH side of that, so two battery state displays.

Same here. It was suggested when we added battery capacity to our previous camper. Seemed like a lot of complexity that was mitigated by also having a generator and solar panel available. I can see the application in marine and aviation but for RV, unless you are in the outback, the juice isn't worth the squeeze IMHO.

 

[vermilye]

I asked Battleborn about adding a new battery to older ones and they suggested that as long as they were within 2 years of each other in age, it would be OK.

 

[Ron in BC]

I'm not a fan of A/B battery switching...

switching to BOTH after one or the other is partially discharged is bad news, the fully charged battery will RAM current into the other batteries, easily 100A or more... and only the 'active' battery is getting charged. I would want a shunt monitor on EACH side of that, so two battery state displays.

It doesn't work that way. It's either or. Use one at a time and if you switch you can go through off without "both". Been doing it for 40 plus years. It's a non-issue.

Ron

 

[Centex]

I'm not a fan of A/B battery switching...

switching to BOTH after one or the other is partially discharged is bad news

That's invited by this switch (Blue Sea 6007)

It doesn't work that way. It's either or.

Yep, with this switch (Blue Sea 600

Pick the one that meets your needs

 

[DT6]

Thanks everyone! I'll order the new battery today, and probably look into adding the switch sometime next summer.

Unfortunately Current Connected no longer sells SOK batteries (except for server rack configurations), so I may have to go with SOK US directly like I did before. It does seem like they have a new support person in place and he has responded much more quickly to my notes than the previous guy who was there.

Now that the BMS on the current batteries is working, they are not running down unexpectedly, so the extra battery will just be there for emergencies as others have noted. We are going to look into adding another solar panel later next year, I just don't have time to deal with it now, but then I can keep an eye out for sales! If I remember right, Ron BC and others have glued a semi-flexible panel to the roof of the 21C, seems like a good way to go.

 

[Mike G]

Aha! The 6008 is foolproof, whereas the 6007 is not. And I am the fool who should have a 6008 if I were doing that....