Multiple Interstate Batteries - Mix and Match

Hey guys. I am currently running a pair of Interstate SRM-24 (690MCA) batteries in my 2003 SAN. I have an extra pair of 24M-XHD(1000MCA) batteries that I would like to run in parallel with the original two. My stereo system consists of a Alpine PDX 1.1000, and two PDX 4.150's.

A few questions.....

1) Is it okay to run these two different batteries together in parallel. In other words, will the different batteries all charge up to 100% even though their capacities are different?

2) What detrimental effects will I impose on my stock alternator? I researched and think that the stock alternator was only 70A (could be 95A, but doubtful).

I'm not looking to be able to blast my music for hours on end, just to give me a longer listening time at lower volumes and not worry as much about starting the boat.

I've never been stranded from playing my music too long, I just finally got around to uncovering some stuff and found these batteries that I had intended to use a long time ago. The timing worked out because I'm doing some troubleshooting with my batteries right now (they're draining fast), but I think that is an issue with my power relay system that I installed last summer. Correct Craft thought that it was smart to run ALL the power for ALL things electrical through the stupid toggle switch next to the driver over a wire that is only slightly larger than 18GA.




Thanks for the help and Cheers!

Eff. The second picture is upside down. Oh well, I'm not changing it. Sorry

If you put those batteries in parallel, you will kill all four within very short order. Not a good idea. The only way to do it is to get yourself an isolator and isolate all of the batteries from each other.

If you want an explanation why, just ask. Otherwise, just take my word for it.

Tuneman; I take your word, but would also like to be made smarter - will you explain?

Ok, here’s the not-so-short explanation in simple terms:

Batteries are made up of a liquid and a solid. The liquid is an acid(with water) and the solid is usually lead plates. Thus the term, lead-acid battery. As a battery discharges (gets used), stuff called sulfates come out of the acid and attach themselves to the lead plates. This is the electron transfer that creates power. Once the lead plates become completely covered with these sulfates, they can no longer transfer electrons and the battery dies.

So, you charge the battery up and the sulfates detach and go back into the acid solution. The quicker you charge, the better, because it allows the least amount of time for the sulfates to remain attached to the plates. If they sit on the plates long enough, they become stuck. Then that area of the plate can no longer be used to transfer electrons. Over time, the plates become permanently plugged with sulfates and that’s when it’ll no longer charge.

Also, when the battery is new, with very clean plates, the electrons have a lot of freedom. So, the internal resistance of the battery is low. As it ages and more sulfates get stuck, the sulfates have less places to go, making it tougher for them and the result is an increase in the resistance of the battery.

Are you following me so far?

Now, let’s add two batteries together. Unless they’re both brand new and come from the same lot, it’s a given that the resistance values of each will be different. (Actually, no two batteries will ever have the same resistance value.) Each battery will always have a different number of sulfates stuck on the plates.

So you charge the batteries. Once one of them becomes fully charged (the weaker one because it has less spots to clear on the plates), the charging will stop. But since each battery has a different number of sulfates, the stronger battery will end up not getting fully charged. And a battery that isn’t fully charged will allow more sulfates to permanently stick to the plates. Eventually, that once stronger battery will fill up with permanent sulfates until it becomes worse than the weaker battery. A charging tug-of-war happens.

The result is that the two batteries will fight each other until they both completely fill up with sulfates and die. This can happen within days or weeks.

I hope that all makes sense.

Yeh, I got that, was hoping to learn the differences between a deep cycle and a cranking/starting battery and how they inter-relate with regards to charging etc. I have a cranking battery, and have wondered about adding a 2nd battery (Perko switch is in the boat already) . When I get serious will do some surfing to find out what I need or don't need.

Thanks

Thanks Tuneman. So if I'm hearing you correctly, ideally you would never want to have two batteries (even same exact one new) without an isolator because you can't count on them charging and discharging exactly the same and eventually they will end up in your so called, tug of war. If that is the case, then why do all the manufacturers (CC Included) just wire them up with a simple perko?

Update on battery issue that started all of this....I took the smaller ones that were in the boat to the Interstate store and they verified that the water was correct and that they took a charge. I think I might just throw the big ones in there anyways. But I still have to track down what is still drawing power when I turn the boat off via the keypad. I've owned 3 CC's over the past 5-6 years, and not once have I ever had a dead battery until all of this nor have I had to charge them. It's gotta be something dumb. Hmmmmm

Deep cycle batteries have thick solid lead plates and starting batteries have thin porous lead plates. The many thin lead plates give you more surface area for more charge, but they can plug up fast with all them sulfates if discharged a lot. Deep cycles can't provide as many cranking amps because of the reduced surface area, but can handle many discharges because the non-porus surfaces of the plates can't plug as easily.

With all that said, ideally you don't want to hook batteries together without an isolator, but you can do it with new batteries from the same lot. I did it with my VLX. With such similar batteries, it'll take a few years before they kill each other. Two new isolated batteries in a boat will probably last you 4 years, whereas two new non-isolated batteries will probably last you 2-3 years. Manufacturers do it to save costs.

Both of these batteries that I have are deep cycles. Just wanted to add that little tidbit. I 'm still gonna go the route of just using two of them. The 1000MCA ones are pretty new and were always kept together.

There is one thing that I'm dead certain of... There is no such thing as a perfect charging system. And, there is no single remedy that is the perfect answer for every boat, audio system and boat owner. We're often forced to prioritize and accept the lesser compromises in any given system. But there are a number of basics that we have to maintain in every system. And one of the basics is... If you're going to series or parallel two batteries on the same bank (one side of the Perko switch) they need to be identical in age, size and type.

You can tolerate different sizes on the different banks (starting versus stereo) because they are used very differently from the onset. They should be the same type in all cases whether AGM or flooded.

David
Earmark Marine

I installed an identical Interstate Deep Cycle when my 06 Sanger was new, two of the same brand and rating, no isolater, no perko, wired in parallel and they are going strong at 4yrs old and counting. I simply carry a portable battery jumper box incase I drain both. I have loaned that jumper box out at the lake many times but have never needed it myself. (knock on wood). As posted earlier, if you are going to do this, starting off with the same batteries will give them a much better chance of a normal lifespan...

Thanks guys. I ended up putting the 24M-XHD pair in last night (replacing smaller ones). They are pretty much brand new.

I think I determined where my power drain was coming from.

At the end of last season, or at the very first of this season, I hotwired the power to the circuit breaker bypassing my toggle switch because the relay went out. I'm sure that I did it as an emergency solution to get on the water that day and forgot about it.

Now I just gotta get a new relay so that I don't have to go ghetto style with my stripped wires and wirenut that I'm gonna use to get on the lake today Maybe I'll post a pic....

Tuneman,

I have a couple more questions for you. I just bought two new batteries, the old ones lasting 3.5 years. Most of the time with these, I kept the Perko switched to "All" both drawing from both batteries and re-charging both batteries when the engine was running or when the maintenance charger was plugged in during storage. But based on your description of batteries working against each other above however, I'm thinking there is a better way that would get more life out of the batteries.

Would it be better to alternate between batteries, i.e. drawing down #1 (while listening to stereo boat stopped for instance), switching to #2 to start, then back to #1 to re-charge it? Then next time out or next time stopped, switch to #2 to draw on, recharging only it when running again?

It sounds like I ought to have a maintenance charger for each battery separately (being I already have one) and use them with the Perko "off" or batteries isolated.

Andy, if you keep your same setup, let them drain and charge together. If you start isolating, as you described, you'll kill them faster because they'll get out of sync faster.

Tuneman/Andy,

I'm in the process of figuring what I'm going to do about on-board charging as well. I have 2 Optima blue tops linked through a Perko switch. I've been charging them independently, but I want to do something else, as I hate having to go switch the charger over. I was also thinking about adding a 3rd blue top for my accessory side, or "2" on the Perko. As I understand, if I wire battery 2 & 3 in parallel and leave them on the "2" of the Perko, they will drain and charge together, correct?

My main question is aiming toward the on-board charger and whether or not to go to a 2 or 3 bank charger. Since the 2 & 3 battery's will be ran in parallel, if I have a 2 bank charger hooked up to battery 2, then it will also trickle over and charge battery 3, correct? So would there be a need to get a 3 bank charger? Would charging be more efficient and better for the batteries on a 3 bank, or will it do me no good to have a 3 bank since 2&3 are in parallel?

I don't know much about charging systems, so I want to make the right decision when it comes to the battery maintenance.

Thanks for your help...

Chance,

I'm not the expert to ask. But, I have a single trickle charger hooked up to my battery 2. When in the garage, I leave the Perko to "All" and plug in the charger. Because the batteries are wired parallel, I'm pretty sure it's trickle charging both batteries. Tuneman, if not, please step in and comment.

Chance,

I'm not the expert to ask. But, I have a single trickle charger hooked up to my battery 2. When in the garage, I leave the Perko to "All" and plug in the charger. Because the batteries are wired parallel, I'm pretty sure it's trickle charging both batteries. Tuneman, if not, please step in and comment.