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Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 3587
Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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I have a 6 bank of solar marine batteries, 6 deep cycle 105A,

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I have a 6 bank of solar marine batteries, 6 deep cycle 105A, and haven't used them much because I needed more of them to be able to utilize them to handle the loads when the power goes out. I want now to add more batteries, 4 more, to make enough wattage that would handle a limited load now for 4-5 hours that it didn't/couldn't before so I didn't use them much.
Is there a reason NOT to add the new batteries with the older ones of the same amps, 105A because the other ones are a year old, even though not used much? I really can't afford to get all new ones unless I have to.
I've heard you don't mix battery types, age or amps, but.....????? name is XXXXX XXXXX I will be happy to assist you with your electrical question. My goal is to exceed your expectations on Just Answer!


1) Yes, you are correct on that it is not recommended to mix the various deep cycle battery elements such as amp-hours, the age and types of batteries.


2) The main areas of concern to not mix are the amp-hours and the battery types, ie, intermixing Deep Cycle with Marine Batteries. The solar industry also recommends to keep the same battery manufacturer as well, but I'm not a firm believer of that.


As long as the amp hours, types and group type are the same, you should not have a problem. You mentioned that yours are 1 year old and I do not see a problem with that. Would be different if you wanted to mix new batteries with 6 yr old batteries.


3) I also have a PV installation at my home and I did some research on this topic a few years ago. The reason being that they recommend to not intermix is that all the batteries should be equal in terms of the battery types, age and amp-hours. If one or more batteries in the existing string or bank has become problematic due to not re-charging fast enough or the battery has reached its maximum life cycle re-charge, is that those faulty batteries can have an immediate negative impact on the new batteries.


The amp hours within the strings should always be equal, this is the most important.


4) As batteries age, their maintenance requirements change. This means longer charging time and/or higher finish rate (higher amperage at the end of the charge). Usually older batteries need to be watered more often. And, their capacity decreases while the self-discharge rate increases.


5) Basically, the rule of thumb is that mixing older batteries with newer batteries, will reduce the life cycle of the new battery as well as the Depth of Charge. Equalization also plays a factor when introducing new batteries into an existing string.




Hope this helps.........If you have any additional questions, let me know and I'll be glad to answer them for you.


Otherwise, don't forget to rate me before you log Off.

The next time you have an electrical question, you can also request for me at:

Kevin and other Electrical Specialists are ready to help you

Hello Dave...... long time no talk. Hope things are going well for you.


Thank you for the positive service rating...........much appreciated!


Take care and have a great evening.............Thanks............Kevin!

Customer: replied 3 years ago.

Thanks Kevin for even caring, this solar system has been rewarding to a point of going forward with something positive, but very, very depressing being in a 3rd world country with limited resources, as well as not speaking the language and few people that know about solar systems. I have simple questions that would be nice to be answered, like can I hook up a "off grid" battery system to the "grid tie" system so I can run certain lighting systems at night when the sun goes down? I don't have enough batteries to run the refrigerators, etc. but do have enough for lights and fans for the guests if the power goes out.

Hello your existing system "grid tied" now or is that something you are thinking about implementing in the future?

Customer: replied 3 years ago.

I have a new "grid tied" system of 27 panels of 230Watts each. Problem is that Nicaragua does not have "net metering" so I can't get the extra that I generate during the day back at night or during cloudy days.

Power goes off a lot where we live, and I have a small hotel on the beach, and when power goes out, especially at night, we have no backup except now I have a 6 battery system (105A 12V deep celled) that is hooked up to 3 of the 230W panels to charge them. How do I hook up the batteries to the main electric panel when power goes out, the "grid-tie" is useless even during the day if the power company is down. I could at least run lights in rooms and restaurant/bar/patio/bathrooms and a couple of fans with the "off grid" system, obviously not enough for air conditioning or pumps or refrigerators, etc.

If I could flip a switch and separate the grid tie to the main panel and tie in the battery bank to the system, turn off all the heavy load breakers and keep all the lights, etc. on, then I could stay in business.

If I could use both systems, charge the battery system when the grid tie is working and over producing.

If I added a couple more batteries I could do night time every night for lights and the minor stuff.

That is the problem with "grid tie" here in Nicaragua, you throw away all over produced energy and don't get rewarded by adding to the grid, and I only over produce from 10:30:am to 2:00PM anyway, so I'm having to use the corporate power companies energy in early morning and afternoon just to meet my load demands.

If at night I only had to use 30-50 11W bulbs and 5-10 45W fans for the rooms, I could do most of the night with battery power, especially at bed time later when I don't need the bar/restaurant lights on at all, just a few.

So do I need different breaker boxes for each system with switches between the two separating the heavy use loads from the battery use loads when the power goes out and I need alternate power from the batteries? 3000-4000 W would do me great during emergencies that happen weekly, just running the lights and necessities, the guests wouldn't know the difference.

Also was thinking the other day of buying some LED string lights to light up the bar/restaurant area's, hundreds of lights on strings that would also run off the batteries, would use very little power, my 6 batteries should easily handle that on a night to night basis and my 3 230W solar panels would do the charging during the day?

I've probably confused the hell out of you Kevin, but I'm desperate to get the most out of what I have here with little help to figure it out.

Hello Dave.... no you have not confused me, all is good Cool


1) I was going to ask if they allowed "net metering" but you beat me to it. Since you are "grid tied" and you want to take advantage of when you experience the temporary loss of commercial electrical power, you will need either an automatic or a manual transfer switch installed at your main electrical panel. The automatic XFER switch is the preferred since it will automatically close your grid tied solar system out to the grid, thus not causing any back feeding to any electrical workers or linemen in the field. However, you can also do this using a manual switch, but then someone needs to be on premise to activate the switch when you want to transfer inverter power being fed from the battery bank. No additional breaker boxes are required to accomplish this, only the XFER switch is required. The automatic XFER switch is also more costly versus a manual XFER version.


2) The automatic transfer switch is basically a high tech version of a double pole double throw switch with built-in relays that will isolate your PV system from the utility grid. Upon the initial loss of commercial power from the utility grid, the automatic XFER switch will sense that via the built-in relays and will automatically transfer your inverter into your main electrical panel, thus isolating from creating any back feed out to the grid. The XFER switch gets installed in between the main electrical panel and your inverter. Once commercial electrical power is restored, then the XFER switch will automatically switch back over to commercial electrical power and not use your batteries. That is a quick summary of how it works.


3) Your battery bank should not have any problem handling the LED string lights, since those are a low wattage.


4) Since you are unable to take advantage of "net metering", you need to assess the financial and determine if it is worth the cost to install a XFER switch if only being used for the loss of commercial power outages. If this will provide convenience to you and your customers, then yes it is worth the expense over the long term. If the outages are minimal, then possibly not worth investing the additional cost for the XFER switch and related labor expenses, etc.



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