Swapping Out Batteries

[Buc]

I bought some new batteries for our trailer, and will be removing the old ones and installing new ones tonight. Batteries are Interstate SRM-24 Deep Cycle.

Am I correct with the following assumptions.

1. I need to have no power going into the battery (solar or shore).
2. I should shut off power to the unit from the batteries.
3. It’s safe to touch the battery posts as long as I don’t connect them together with anything metal.

Anything else I need to keep in mind? I’m planning to mark which cable goes where and take a before picture for reference.

 

[TheLooks]

Put up a picture of the cables. Many times factory or previous owner installed batteries are not cabled in the most efficient way. This can hurt the life of your batteries.

 

[Buc]

 

[TheLooks]

The way it is wired you are pulling and charging the one battery with the cables on it from and to the rig. Move the negative cable to the far left in the picture to push and pull power from both batteries equally.

 

[Buc]

The way it is wired you are pulling and charging the one battery with the cables on it from and to the rig. Move the negative cable to the far left in the picture to push and pull power from both batteries equally.

Are you referring to the negative cable in the middle?

 

[TheLooks]

There are 2 negative cables and one positive. I would move both negative cables to the left. This makes the 2 batteries act like 1. The power in both directions must travel thru both batteries equally. The battery on the right is doing all the work and getting charged the most.

 

[Buc]

There are 2 negative cables and one positive. I would move both negative cables to the left. This makes the 2 batteries act like 1. The power in both directions must travel thru both batteries equally. The battery on the right is doing all the work and getting charged the most.

That makes more sense. The way you worded your response suggested moving one cable.

 

[Buc]

Would the way it’s currently wired lead the battery power indicator inside the trailer to give funky readings? It’ll sometimes go from empty to 1/3 to 2/3 to empty to 2/3 to full in seemingly random order.

 

[Buc]

Anyway… New batteries installed. We’ll see how camping with no shore power goes this weekend versus the past two.

I couldn’t change the position of those two negative lines since they aren’t long enough to reach. Is that crucial enough to go back and extend them at some point?

 

[TheLooks]

There are many configurations for multiple batteries. You may never notice the difference in a 2 battery setup. I automatically look for the best configuration now after some schooling on it. You could flip the left battery around and then only need a longer positive to reach.

 

[Buc]

Seems to be all good now. We camped in Rocky Mountain National Park this weekend for two nights with no power. We used the lights, fridge and heater fairly normally. The power level went from 100 to 78% the first night. We were mostly in the shade, and some afternoon thunderstorms rolled in on Saturday, so the power was at 85% went we went to bed, and dropped to 68% overnight.

Speaking of shade, this pull-through site was hard to get out of yesterday.

 

[TheLooks]

It is not something you would notice, it is a long term effect of discharging and charging one battery more then the other. It was just a suggestion that you can confirm with an internet search. Many would not bother to change it as it is more noticeable with multiple batteries. And some people are driven to get everything perfect......

 

[Kevin D Pem]

View attachment 20135

@TheLooks are being nice!!!

As soon as the batteries become unbalanced the battery on the right will start boiling and start self distructing while the one on the left will start sulfating. With this set-up I give your new batteries 6 months tops.

I would try to make the positive cable reach the positive post on the battery on the left. If I couldn't stretch(reroute) it, I would buy a 1ft cable and bolt and tape it up to extend it. I might even try Joe's bottle shrink wrap trick to cover the joint.

 

[Bigblockyeti]

The batteries are wired acceptably well in parallel, I would change nothing. That the starboard battery has an extra 16" - 18" of substantial gauge wiring running to it means that under an extreme power draw, it could be used 99.99% of the capacity of the port battery running at 100%. Ohm's law does apply but to a very, very, very small amount.

 

[Kevin D Pem]

The batteries are wired acceptably well in parallel, I would change nothing. That the starboard battery has an extra 16" - 18" of substantial gauge wiring running to it means that under an extreme power draw, it could be used 99.99% of the capacity of the port battery running at 100%. Ohm's law does apply but to a very, very, very small amount.

https://www.outbackpower.com/downloads/documents/energy_storage/northstar/northstar_blueplus_manual.pdf

If, and that is a big If! The battery industry is wrong, and you are right, then the wiring diagram #8 in this PDF is just bull!!!

All I can tell you is this particular manufacturer warranties there batteries a very long time, if you follow their advice, and not at all if you don't!!!

By the way! I am still a student in this life! I welcome learning something new!

 

[TheLooks]

I had this debate in solar class and I sided with Bigblockyeti about the insistence that the cables be exactly the same length. But in a situation like this it is not so much the length as it is the point of draw and recharge. It will effect the battery on the right much faster with this wiring scheme. I would change it. Minimal cost.