Which of these batteries?

[TnK]

I know…I know…I should be using LiPo4 batteries. Especially since I have solar.
But it’s not in the budget right now. Keeping that in mind here’s my choices (because I have these batteries on hand).

Vehicle: 2022 Melbourne
Current batteries with maybe 2 hours of use are 2 Harris Professional Plus 24D140 Lead Acid Deep Cycle. Having 140 min. RC.

My alternative is a 2 years old (but never installed) group Super Start from O’Reilly Auto Parts 31DCMJ Lead Acid battery with 845 min. RC.

Now I cannot fit all 3 not the battery compartment in the step but…I could replace both of the group 24 with the 1 group 31. Weight difference would be minimal but I’m thinking I would gain a substantial amount of useable capacity
(figuring 50% of what’s listed it would be 140 (50% of the combined group 24 batteries) vs 420)).

I haven’t got the final measurements yet but it might even be possible to squeeze the group 31 AND 1 of the group 24 batteries in there together.
My questions are…
1. Am I correct in my figures?
2. How would it affect my solar system?
3. If it does effect it would I need to reprogram my controller?
4. If I can fit one of each battery in the space, would it be advisable to mix the 2 brands since they are both the same type of battery?
5. Should I just shelve the idea until I can purchase 2 of the LiPo4 batteries?

[cpd1343]

NEVER mix and match batteries!! They should both identical in every respect: age, size, manufacturer, etc.

I used 2 of these:

https://www.interstatebatteries.com/...ategoryid=true

[dvspl]

When I looked up the Super Start Group 31, the specs I found said it's a 105 AH battery rated at 210 minutes of RC. The Harris Professional shows 140 minutes of RC and is likely about 80-85 AH. So in theory the two Group 24s should give more capacity. In reality, I suspect you'll get very similar performance from two of the Group 24 vs one of the Group 31. You could use one of each in a parallel setup for slightly more capacity but this would put a heavy load on the smaller battery and might lead to overcharging/boiling. I wouldn't do that personally but you could choose to if you're planning to replace them soon anyway and the present setup doesn't give you enough capacity for your planned trips.

Reserve capacity (RC) isn't really a very good prediction of deep cycle battery performance in RVs since it is measured at 25 A discharge rate which is well above the DC load in a typical RV. Lots of good info on this topic at Battery University. Here's one link: https://batteryuniversity.com/articl...asure-capacity

[ait109]

You referenced the wrong number as dvspl mentioned - the 845 value is the CCA which is not relevant. Your Group 31 battery is only 210 RC, which means that keeping your two Group 24's with 280 total RC is probably better. I say probably because RC is an imperfect measurement of battery performance.

As cpd131 said, not a good idea to mix batteries that aren't the same spec.

I also have the same battery set-up as you in my 2022 Odyssey. I figure I have about 75 Ah of total usable energy when fully charged. I decided that before I do any changes I should install a shunt-based battery monitor so that I know exactly how much energy I use to help me inform my energy needs.

In my mind these upgrades is a slippery slope: I want a bigger inverter (to run microwave, coffeemaker) > Use Lithium to get more battery capacity > Need DC-DC for alternator > Need new Converter > More Solar. Plus where to put the batteries is another important factor. All-in-all this is a major upgrade that needs some good thought.

[TnK]

Yeah…I’m planning a total upgrade of the system but that’s a ways away yet.

[Northwest Bob]

I use two identical 12 volt AGM batteries wired in parallel as my house batteries on my Jayco 31DS. They seem to last quite a while when boondocking. At worst, I have to fire up the generator for a while to supply power and charge up the batteries.