Lithium and AGM together

[BBug]

I have been wondering, and I know that there will be many on this site who will know. If one battery in a 24 volt system, run by AGM batteries ,were to  die, what would be the pros and cons of putting a lithium in as a replacement. I know about the weight, costs, and the up front pros and cons, I was wondering about compatibility issues with the two types, if any.

[Woody B]

If one 12 volt battery in a 24 volt system dies you'll be better off to replace both, regardless of chemistry.  

[MN Fisher]

Don't mix chemistry's - in fact, if one battery fails it's best to replace both as Woody says...you want both batteries in a 24v system to be as identical as possible. This not only means AH/Reserve, but also date of manufacture.

 

If you want to go Lithium - just get a 24v lithium battery to replace both old AGMs.

[BBug]

You say not to mix chemistry's, just curious but what happens if you do? I know that they charge and discharge differently and I get the logic of replacing both at the same time. But, for the sake of understanding, do you have more information  as to why or better, why not? 

[MN Fisher]

Different chemistries have different storage/discharge properties. Mixing types can cause things like quicker discharge, over-heating, or damage to the BMS on the lithiums as they try to compensate for the lead-acid battery connected (Wet-Cell, Gel-Cell and AGM are all lead-acid batteries).

 

Mixing an old and new battery, even of the same type/model, will cause the system to 'average out' and reduce performance...that's why replacing both (all) batteries in a multi-battery system at the same time is recommended. That holds true whether they're connected in series or parallel.

[BBug]

You say not to mix chemistry's, just curious but what happens if you do? I know that they charge and discharge differently and I get the logic of replacing both at the same time. But, for the sake of understanding, do you have more information  as to why or better, why not? 

Ok that  makes sense. I have heard that you really don't want a lithium to go "bad".  This is very helpful. Thanks

[casts_by_fly]

Also, lithium is a higher voltage. Both are nominally 12 volt but lithium is 13.6V while lead acid is 12.8 I think. Then lead acid voltage drops over time. Effectively what you’ll do is push charge from the lithium to the lead acid constantly. Same as mixing lead acid and agm but to a lesser degree. 

[BBug]

Perfect ,I wasn't thinking about the BMS taking input from the other battery. I am not in need of new batteries, yet. I am just looking for knowledge and information on different battery arrangements. Casts, when you mentioned the push from one source to the other, with lead acid and agm, is there an issue other then drawing the more powerful battery down quicker? Would the stronger battery get overheated trying to feed the motor and the weak battery or would it just wear down sooner?

 

[GaryH]

As already mentioned. There’s only one correct answer to your questions. If you’re going to replace your battery/batteries go with 2 of the same type and age. I run lithiums and all 4 are the same age. The same would go when I ran agms. Battery safety is paramount on a boat don’t look for shortcuts. 

 

 

[Tennessee Boy]

Combining an old lead acid battery with a more capable battery in series is kind of like combining an old mule with a stronger younger mule in a team.  The young mule will be held back by the old one so the strength of the young mule will be underutilized.  The old mule will be pushed beyond it’s capability by the young mule and probably won’t last long.  Combining a new Lithium battery with an old lead acid battery is like combining a thoroughbred horse with an old pony.  

 

This is less of a problem when combining old and new Lithium batteries because the BMS in the old battery will cut off before the battery is exhausted.   The new battery would still be underutilized in this scenario.  The manufacturer of my Lithium battery (Battle Born) suggests not combining a new battery with one more than 4 years old.

[Deleted account]

Sometimes I reverse the AA batteries in the remote instead of getting up to get new ones in order to change the channel and it works...  

[airshot]

On 2/12/2023 at 10:09 AM, BBug said:

You say not to mix chemistry's, just curious but what happens if you do? I know that they charge and discharge differently and I get the logic of replacing both at the same time. But, for the sake of understanding, do you have more information  as to why or better, why not? 

Ok that  makes sense. I have heard that you really don't want a lithium to go "bad".  This is very helpful. Thanks

The problem is, when the two batteries do not match then they will fight, you do not want to tick off a lithium battery, because when they are not treated the way they want....they catch on fire...quickly..very quickly...then they burn white hot and burn up anything within there reach !!  I have used them for years and they are great, but do not make a mistake with them, nor cross them as you will pay !!  I have witnessed personally a lithium battery get hooked up to the wrong charger.  The owner realized this and pulled the plug within seconds of realizing the mistake.  In seconds the battery turned to a white hot fire, burnt thru the bench top, dropped onto a concrete floor and burnt a crater into the concrete floor all within less than 15 seconds !!!!  And your fire extinguisher wont put it out. !!!  It needs to be smothered in sand....  which of course we all carry on our boats !!!  Can you imagine all this happening if you were to make a simple mistake in your boat ???

Lithium are great but not worth the gamble in a boat!  Now there is a much safer version called a Life04 or something like that, it is much safer but also more expensive.  I am considering these when my agm batteries need replaced.

[MN Fisher]

1 hour ago, airshot said:

you do not want to tick off a lithium battery, because when they are not treated the way they want....they catch on fire...quickly..very quickly...then they burn white hot and burn up anything within there reach !! 

That's true with the old Lithium-Ion batteries, but the newer LiFePo4 batteries are much safer. The worst you can probably do to them is fry the BMS, which will basically make the battery useless.

[jhoffman]

New lithium's will allow you to run 12/24/36 out of a single battery, you just need the right capacity

[BBug]

lots of good info here. I already run the new style LiFePo4, by itself, for electronics only. I have the charger that is required and I am very pleased with my set up. I was just asking the question for a better understanding. I was told by the folks at MK that if you run lithium batteries on the Ultrex, that you should stay under 80% power. I believe they meant for long runs like spot lock in a fast current. Anyway, I still have fairly new AGM's and am not really in the market. So Thank you all for the discussion, and input. 

Once again for the sake of knowledge, I also have been told that Yamaha does not cover warranty issues in regards to using lithium batteries as starting batteries. If worse comes to worse and one  is on the water with a dead cranking battery, could you use the lithium to jump start with cables? Once again this is just for knowledge. I have the agms that I can take out of series to get it running if I needed to now. However in the future, I may run lithiums on the trolling motor so that would be all I would have.

Thanks 

[MN Fisher]

Just now, BBug said:

If worse comes to worse and one  is on the water with a dead cranking battery, could you use the lithium to jump start with cables?

If the lithium is rated as a starting battery, then yes. Most lithiums are rated for deep-cycle only and the BMS prevents high-amp discharges of the type needed to start a motor.

[BBug]

understood. again, thanks