Mixing old and new batteries. Your thoughts?

[Portage_Bay]

I am thinking of adding two batteries to a six battery bank. I know it is generally not a good idea to mix old and new. But the six batteries were purchased and installed 24 months ago and have been very gently used. Mostly dock hopping or tied to the home marina on a charger. The have just 4 nights on the hook. 2 nights each time with gen run time during the day to keep things charged up.

The boat's complete battery system is the house bank of six GC2b batteries in series parallel, a single 8D to start both Cat 3208 NAs and a group 27 to start the generator.

My thoughts are to follow Rod's thinking in this article on the 1/2/Both switch where he discusses using the house bank as the primary start bank for the mains. I would add two GC2bs where the aging 8D is. Increasing the house bank and eliminate the dedicated start batt for the mains.

I'd rather not throw out six good batteries to buy eight more.

The gen start batt would be upgraded to a group 31 that could be used to start the mains in a pinch. I also pack a jump pack to help get the gen started if need be. And, because the gen is old a Honda portable just in case.

Those familiar with the 3208s know that they easily and reliably.

 

[Brooksie]

If it were me, I would look at the other side of the equation. Adding more storage for 4 nights on the hook with a generator no less seems like you have some power hogs aboard. Starting with your refrigeration and lighting I would try to knock amp hours off your load. I know everyone & every boat is different, but I have anchored out every night for 5 months straight w/o generator on 2 golf cart & 1 start battery including a small refrigerator.

 

[Portage_Bay]

If it were me, I would look at the other side of the equation. Adding more storage for 4 nights on the hook with a generator no less seems like you have some power hogs aboard. Starting with your refrigeration and lighting I would try to knock amp hours off your load. I know everyone & every boat is different, but I have anchored out every night for 5 months straight w/o generator on 2 golf cart & 1 start battery including a small refrigerator.

Good input but my living on the hook loads are not large by today's standards. A modest refer. No AC. Most lighting converted to LED. Very light use, as in almost none, of TV, audio etc while on the hook. Inverter is turned off unless needed.

The problem is mostly underway not anchored. Two OEM 55 Amp alternators, I like to run low RPMs so I've measured output at about 27 Ams per alt max output. One feeds the house bank, the other feeds the start batt. On the house bank first back out 7 amps for the energize to run solenoid. Then back out the normal running loads. If in restricted vis the radar as well. The charge current to the house bank is minimal. If I want to bring the freezer down using the inverter I may actually be going backwards while underway.

First steps will be upgrading the alternators with 105 Amp, the largest that will fit on a 3208, controlled by Wakespeed WS500 allowing me to tie both alt outputs into the house bank and get the maximum benefit of charging.

I could then use a DC to DC charger for the start batt or eliminate the start batt all together increasing the now only bank. That is what triggered the question.

You may be wondering why I don't use the gen more. It's old, not as reliable as I'd like, parts are made of unobtainium. Cost to replace will be about $20K all in. Long term, the next time I spend weeks trouble shooting then sourcing parts, I'm looking to eliminating the gen and have a 2nd bank were it now sits.

 

[koliver]

I am thinking of adding two batteries to a six battery bank. I know it is generally not a good idea to mix old and new. But the six batteries were purchased and installed 24 months ago and have been very gently used. Mostly dock hopping or tied to the home marina on a charger. The have just 4 nights on the hook. 2 nights each time with gen run time during the day to keep things charged up.

The boat's complete battery system is the house bank of six GC2b batteries in series parallel, a single 8D to start both Cat 3208 NAs and a group 27 to start the generator.

My thoughts are to follow Rod's thinking in this article on the 1/2/Both switch where he discusses using the house bank as the primary start bank for the mains. I would add two GC2bs where the aging 8D is. Increasing the house bank and eliminate the dedicated start batt for the mains.

I'd rather not throw out six good batteries to buy eight more.

The gen start batt would be upgraded to a group 31 that could be used to start the mains in a pinch. I also pack a jump pack to help get the gen started if need be. And, because the gen is old a Honda portable just in case.

Those familiar with the 3208s know that they easily and reliably.

Sticking to the question of old and new being mixed, with the gentle usage you describe, I would not hesitate to call the old batteries "almost new" and simply monitor their health going forward.

The Q posed by Brooksie is also valid. What are you carrying that consumes so much power that you need to increase the size of your bank?
You may have an aging start battery, and when it is done, you may want to consider some other setup, but why this setup?
You already have 3 more batteries than I have, though I don't know what loads you carry.

My setup, that has worked for well over 20 years, is:

A single 4D on a separate circuit that starts two main engines and 1 generator, is charged at the dock or generator through a Xantrex MS2000 charger, in motion through the port alternator. This is NOT connected to the House bank through a 1/2/B switch.
A house bank of 4x6vGC FLA batteries, 220amp hours each, for a bank of 440 Ah at 12v. Also NOT connected to the unused 1/2/B switch that became redundant when I changed from an AC/DC fridge to DC only and got rid of the #2 House bank. I also have a battery combining solenoid in the unlikely event that I need the house bank to supplement starting power. In 27 years I have never needed this feature.

Unless you have loads that are significant, that your present setup is not capable of continuing to satisfy, why would you want to add to the House bank.

Just read your second post. Once you have adequate alternators, on an adequate "smart" regulator, your problems with overloading while underway will go away, whether you change batteries or not.

 

[Portage_Bay]

Thanks for everyone's input. This is very much a thought exercise to help plan the final DC system. As to why I'm considering it. Simplicity and cost. A new 8D plus DC to DC charger? Or add two new batteries to make a bigger one thing does it all bank? Better to make that decision before I upgrade alternators and regulators.

 

[Brooksie]

Yes, I understand. And I do have two alternators on my engine. One 35A connected to starting battery and the other 100A for the two 6v T105's.
Charging one bank w/ 2 alternators is problematic b/c the voltage from one causes the other to "think it's not needed". That's what happens if, for some reason, I put my switch on BOTH, one alternator stops charging for all practical purposes

 

[caltexflanc]

Yes, I understand. And I do have two alternators on my engine. One 35A connected to starting battery and the other 100A for the two 6v T105's.

So you use your main engine to charge your batteries while on the hook?

Balmar makes a product to charge batteries from two alternators. https://balmar.net/centerfielder-ii/

 

[Portage_Bay]

Yes the Centerfielder is well respected. However the Wakespeed WS500 is newer more advanced and will work better with lithium. Which I will probably use if I eliminate the gen.

So you use your main engine to charge your batteries while on the hook?

Balmar makes a product to charge batteries from two alternators. https://balmar.net/centerfielder-ii/

 

[alormaria]

I'm agin it.

 

[Brooksie]

So you use your main engine to charge your batteries while on the hook?

Balmar makes a product to charge batteries from two alternators. https://balmar.net/centerfielder-ii/

Yes, but it only works with their outrageously expensive regulators which probably only work with their outrageously expensive alternators.

 

[Brooksie]

https://gcaptain.com/fire-and-gas-e...ZeigIYENlzo5NFMZNTT8qjWRQ8f6jxCGE9zMWOfRvN94E


https://gcaptain.com/safety-concern...4ef03-736c1ce7b5-139871625&mc_cid=736c1ce7b5&
mc_eid=933bf3c19d


https://gcaptain.com/battery-powere...lkn3bC7Nr7c0Gu0VMknVCJ2zhT71UlCwqq44C8NoCCK6I

 

[sean9c]

If the articles are correct it's different battery technology. Lithium Ion was used on the ferry. I think just about anyone considering Lithium batteries for their boat is looking at Lithium Iron Phosphate which does not have the thermal runaway issues of Li-Ion

https://gcaptain.com/fire-and-gas-e...ZeigIYENlzo5NFMZNTT8qjWRQ8f6jxCGE9zMWOfRvN94E


https://gcaptain.com/safety-concern...4ef03-736c1ce7b5-139871625&mc_cid=736c1ce7b5&
mc_eid=933bf3c19d


https://gcaptain.com/battery-powere...lkn3bC7Nr7c0Gu0VMknVCJ2zhT71UlCwqq44C8NoCCK6I

 

[av8r]

A different approach would be to match the alternator speeds (and output) to the lower engine speeds with smaller pulleys on the alternators. Higher alternator rpm will increase the output current early in the charging cycle but won’t make up for the internal regulator limitations.

 

[Portage_Bay]

The alternators I'm interested in are fitted with the smallest pully that will reliably run a vee belt.

A different approach would be to match the alternator speeds (and output) to the lower engine speeds with smaller pulleys on the alternators. Higher alternator rpm will increase the output current early in the charging cycle but won’t make up for the internal regulator limitations.

 

[DDW]

Yes, but it only works with their outrageously expensive regulators which probably only work with their outrageously expensive alternators.

Their regulator is priced at about the market for one of similar spec (there are several other brands). Their alternators on the other hand do seem to be an outlier.