Which of the 2 batteries

[Cgolf]

So in my 16 foot Alumscraft Lunker I run an 24 volt 80 lb thrust Minn Kota Terrova. When first installed they put two size 27s in. Well all I can say is despite a lot of effort and curse words the 27s didn’t fit right. the last two sets of batteries were size 24s. 
 

Unfortunately during the pandemic I had one choice of batteries and they were not good. I do have a 10 plus year old Minn kota onboard charger that I need to research on the AGM side. 
 

Below is the battery compartment. 
 

 

Here is the 24 DC battery 

[Cgolf]

Here is the AGM

So is the AGM gonna be that much better? When on a week long trip I have an outlet on the dock to plug in to to top the batteries off. Also if the AGMs are better do they justify the extra cost which may include a new charger?

 

thanks cgolf

[Dirtyeggroll]

AGM batteries tend to have a little longer lifespan, don't require any water filling and can be mounted any position. Only you can decide if that's worth the cost or not. 

 

A new charger ain't cheap.

 

Personally, I'd keep buying the cheapest battery possible and make sure to practice good charging habits to promote longevity until lithium comes down a bit more and then upgrade charger and to a lithium battery.

[Bird]

They are maintenance free, a tad lighter and have a slightly longer service life than lead acid.

Lithium is the way to go if you can swing it. Imo

[airshot]

I have a 16' Sylvan with a 55lb MinnKota, 12v.  Wiredvto two group 31 batteries, AGM type, can troll all day 8 hrs with no problem. 

[Way2slow]

AGM require less maintenance.  They generally have a longer cycle count (service life) but will not have the Reserve Minutes/Amp Hour capacity of a similar size flooded cell battery with service caps on them.  With both AGM and Maintenance free batteries, they have to reduce plate size to make room for the glass mat material in AGM or extra electrolyte in maintenance free non AGM batteries.  The less lead in the battery, the less capacity the battery has, and the lighter the battery will be.  AGM's are a little more sensitive to the charging voltage and maintenance float voltage but unless you charger is extremely old, it's probably suitable for AGM.  

Now, with all the said, I usually don't buy AGM trolling motor batteries because of the reduced capacity.  Don't let the higher MCA/CCA miss lead you.  That means absolutely nothing when used as a deep cycle TM battery.  That's stickily just extra ump it has for cranking the big motor. 

You want to look at the Reserve Minutes (RM), the higher that number, the more run time you will get on the TM.  If it does not list the RM, then look for the higher Ah capacity.

[Jig Man]

If room is a factor, AGMs don’t have to be mounted in the traditional way.

[Way2slow]

Yes, AGM's can be laid on their side or stood on end.  I don't have the documentation to prove it, but somewhere in the past when I was messing with these things on a daily bases, I was told when mounted that way, it reduces their capacity approximately 10%.  Some of the electric pallet jacks I worked on had them mounted on end so they so they could make the battery box narrower.   

[GaryH]

If you can afford it, Lithium with get you longer cycle count and less weight along with being able to run down much lower without losing power.

[Bankc]

In your situation, no.  AGM wouldn't be worth it.  If you wanted an upgrade and needed to replace the charger anyway, I'd go lithium.  Lithiums can also be mounted sideways or whatever way you want.  

 

If you can't swing an upgrade to lithium, I'd stick with traditional lead acid.  If you want quality, commit to quality.  If you want saving, commit to savings.  Trying to compromise between the two will get you neither.  

[Cgolf]

6 hours ago, Bankc said:

In your situation, no.  AGM wouldn't be worth it.  If you wanted an upgrade and needed to replace the charger anyway, I'd go lithium.  Lithiums can also be mounted sideways or whatever way you want.  

 

If you can't swing an upgrade to lithium, I'd stick with traditional lead acid.  If you want quality, commit to quality.  If you want saving, commit to savings.  Trying to compromise between the two will get you neither.  

I will stick with lead acid then. I am not 100 percent sold on lithium as being the safest alternative. Probably due to using the Lipo batteries for RC planes that were temperamental especially during a crash. Having to charge batteries in a burn proof sack is not a great memory when putting lithium batteries in my boat. 

[MN Fisher]

35 minutes ago, Cgolf said:

I will stick with lead acid then. I am not 100 percent sold on lithium as being the safest alternative. Probably due to using the Lipo batteries for RC planes that were temperamental especially during a crash. Having to charge batteries in a burn proof sack is not a great memory when putting lithium batteries in my boat. 

RC, Phone, AA and AAA rechargables are Lithium-Ion...which does have the bad rap of getting hot and burning...why you don't see them in heavier duty usage anymore.

 

LiFePo4 is much safer than Lithium-Ion...if I had the money, I'd have no compunctions about going LiFePo4 in the boat.

[HenryPF]

AGM vs. LiFePO4s

 

Everything is hyperlinked.

 

A 70ah Group 27 AGM is around $180 (your posts)

Two batteries for your 24v system, $360

 

You should discharge a wet cell or agm battery to no more than 50%

This gives you for a 24v system 70ah usable between charges.

 

A 50ah LiFePO4 battery is around $200.

Two batteries for your system, $400

 

You can discharge a LiFePO4 battery to around 100%

This gives your system 100ah usable between charges.

 

LiFePO4s seem the way to go, but the on-board charger, $129 (2 bank, 5 amps per bank) or $220 (2 bank, 10amps per bank) will be your breaking point.

 

So: $360 for two new group 27 AGMs, or $620 for 2 LiFePO4s w/battery charger at 10amps, $530 for 2 LiFePO4s w/battery charger at 5amps.

 

$260 or $170 will solve your issue of space (50ah LiFePO4s are much smaller and lighter) and give your more of usage. Charging time is up to you.

 

However LiFePO4s should not be charged in the cold (30 degrees or less) but discharge is the same in the cold as AGMs at -30% less ah overall.

 

I am not choosing some crazy 10 year warranty LiFePO4s, just 5 year like the AGMs, price out LiFePO4s with a bluetooth functionality or LiFePO4s with BMS cold charging protection.

 

 

 

 

 

 

 

 

 

 

[Tennessee Boy]

I need to disagree with some statements made in this thread.

 

First -  When you run two batteries in series you double the voltage but not the amp hours.  Running two 12 volt 50 ah batteries in series will give you 24 volts and 50 ah. 

 

Second -  The lithium industry likes to say that you should never discharge a lead acid battery below 50% of capacity therefore the capacity of all lead acid batteries is actually half what they claim.  They also state that this is not true with LifePo4 batteries.  This is not completely factual.  With both battery technologies,  the depth of discharge affects the life of the battery.  Lead acid batteries are affected more but it is wrong to suggest that something terrible is going happen to you battery if you ever go below the 50% threshold.  Many people accepted this marking hype as fact.  Here is a good video that explains this issue.

 

 

[Way2slow]

Tennesse Boy is right, there is a whole bunch of BS in HenryPF's post.  It's all about making the numbers favor a certain company's product.  First off, a 70Ah group 27 is about the bottom of the line size battery.  Good group 27's are typically 105Ah,  27TMX_Trojan_Data_Sheets.pdf (ctfassets.net).  A lead acid battery can easily be discharged to 25% charge without damaging the battery.  The only thing deep discharging below 50% does is reduce the cycle count. 

Lithium batteries are on the same advertisement hype as spiral wound AGM batteries.  10 years of experience running them with RC planes and helicopters has taught me is will still be a long time before I spend the money or trust them enough to run in a boat.