Lithium Battery Capacity

I'm considering upgrading to a pair of Valence 40ah lithiums, these are used medical batteries that are fairly inexpensive.

I've been doing some reading, and saw (from lithium sellers, mostly) that lithiums offer 100% of available capacity, while lead acids offer only 30-50%. That would mean my current ~100ah batteries have a useful output of 30-50ah, so the smaller lithiums are equal.

Is that true though? I always thought amp hours were calculated using the normal discharge limits of the battery, not pulling it into damaging territory.

It really depends on what you are using them for. Mostly it is BS. You can generally use 70% of a standard lead acid battery. The difference is that the voltage on a lead acid slowly decreases as it discharges while a lithium stays fairly flat then drops off suddenly.

The idea that draining a lead acid below 50% damages it is 100% balogna.

Lithium is a good source of power, my only concern is you have a very small window of when its got output and when its over, and I mean now.

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Originally Posted by CatFan

It really depends on what you are using them for. Mostly it is BS. You can generally use 70% of a standard lead acid battery. The difference is that the voltage on a lead acid slowly decreases as it discharges while a lithium stays fairly flat then drops off suddenly.

The idea that draining a lead acid below 50% damages it is 100% balogna.

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That's kind of what I thought.

I'd be using them for a 24V Terrova, I've got two Walmart 29DCs in there now, 100 amp hour batteries. One of them is a few years old and I'm not sure that it'll make it through the season.

Lithium dealers make it seem like you can downsize quite a bit and still have the same capacity, but it doesn't seem to add up to me. I don't want to get those 40ah batteries and end up with way less run time.

ACC Crappie Stix just put out a good read on traditional batteries vs lithium’s.


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You will find that lithium battery manufacturers and sales people will try and sell you on the weakness of wet cells over lithiums maintaining a constant voltage charge until a lithium has used around 80% of its amps and then the voltage will start to drop. I read that in all the forums. What I don’t hear is the argument of AGM batteries vs Lithium in voltage drop issues. There aren’t a lot of discussion and maybe it’s cause the guys using AGM’s haven’t decided to switch to lithiums as of yet. There are a heck of a lot of guys that tourney fish using 2-50 amp lithiums for 24 volt TM’s and 3-50amp lithiums for their 36 volt trolling motors and they charge them each time they use them on a daily usage. However,,it depends how much your using your trolling motor. If your constantly longlining jigs or Crankbaits all day long then go with 100 amp batteries. Most that do,,only have to charge them every couple of days of serious fishing that way. What sells me in the lithiums I have,,,is no voltage drop means I have no issues with my electronics if the voltage were to drop using wet cells. I have as strong running trolling motor from the time I turn it on,,till the time I turn it off and never have to turn the speed up as I used to have to do in using wet cells. Never have to worry if the batteries need water. Have no issues with corrosion of battery terminals either. Super light weight vs wet cells. Charge alittle quicker. Never a voltage drop when stored for any length of time. My lithiums have not lost 1 amp stored all winter and don’t need charged when I finally have no ice and will hook the boat up next week to fish. And at 71,:the lithiums will outlast me in all probability and I will never buy batteries ever again.

8 yr warranty on my Ionics, 10 yrs on Battle Borns

I just ordered a couple of 60 amp lifepo4 from Amped Outdoors. I bought them cause they are compact and lightweight. I will be replacing the Everstart 27s which have been in use since 2013. At my age, cost is not relevant.

Cevans, very impressive informative information you gave on the lithium battery vs wet cell. I am interested in moving from old technology to new. But at 61 I find myself a bit skeptical as always. But your response on this has really got my attention and thank you. But I do have a few questions if you find time to answer them. What type battery charger do the lithium batteries take? How long does it take for them to charge up? Can my same on board charging system be used that I use for wet cell batteries? The other selling point to me is I still fish out of heavy aluminum boat this is due to fishing rivers with lots of unexpected floating logs that can be just under the water. Battery acid and aluminum can be an issue if not contained.
Finally what’s the best way to figure out exactly what you need and how to keep expenses down while making the change? Oh in one more how often do you have to replace these? On wet cells I can get anywhere from two to five years out of my wet cells. That really depends on up keep and brands.


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I was using a ProMariner 20 amp 2 bank charger for charging wet cells..Reset it to charge AGM batteries and it charges my Lithiums to 100 percent. Charging each battery at 10 amps takes a couple of hours when at 60-70% to 100%. With lithiums,,you do not have to charge them to 100% if you don’t want to. Sometimes after 2 days of running trolling motor,,I may be down to 45-50% used. I also use a 1 bank NOCO lithium battery only charger for the 100 amp electronics and to run/start my 25 electric start motor. It only drops about 20 percent per day usage as I don’t run long distances with motor to charge it a lot. Electronics on boat are a 9 MSI g2n, 10 MDI g3n, 12 MDI G4N, mega 360, network, gps puc, trim tilt plate, 25 motor, lights in boat and builge pump. I don’t have a live well as use cooler for fish. I also plug in phone and iPad most days. A lot of wet cell chargers that have a AGM setting on them will charge certain lithiums, you just have to check with the manufacturers of them. You can also use a 20 amp, 30 amp charger per bank in lithiums to speed up charging times. I could have gotten cheaper batteries from Amped but wanted the phone app that Ionic has Bluetoothed into their batteries. It gives me total info including hours/minutes left in them while using, how many amps I am pulling or charging, how many hrs/minutes left to charge when charging. Monitors each cell constantly, also gives battery tempature and voltage your charging at as well as volts your pulling at while everything turned on and a,bit,of other info also. Right now,,I think due to manufacturing issues due to Covid 19,,and demand,,,battery prices are not dropping and remaining constant. Look for deals and discounts in buying batteries. Also,,lots of chargers being manufacturerered today and more being considered and made as time progresses at all price ranges. One other thing about lithiums,,no liquid in them,,so if needed,,you can mount them on their side, upside down, or stacked on each other. These new lithiums now have improved BMS management system installed in them to prevent over heating, fire, and over charging as well as are managing the output in a constant voaltage and will automatically shut down the battery or charging. One other thing about a batteries BMS system. If using a 12 volt trolling motor, you can hook a 100 amp battery, a 50 amp battery, a 30 amp battery in parallel,,,and the bms will equally charge all at the same time as well as you can use them on a trolling motor at the same time and for example,,the 30 amp will last as long as the 100 amp hooked in parallel. Same if I hooked a 50 amp in parallel to a 30 amp for electronics giving me 80 amps to run electronics as the BMS systems works to equal out the used amps when using or charging. I may be using 2 amps of the 50 while only pulling 0.5 amps out of the 30 keeping each battery equal in the amount of power left in each. I have been experimenting using different battery sizes in finding this info out and discussing this with Ionic and it works as well as they confirmed this prior to my experimentation so the combinations are unlimited when in parallel. If buying a 24 volt or 36 volt lithium,,,you will need a 24 volt or 36 volt charger.

if you call some of these manufacturers and sellers,,they can pretty much tell you what you can get away with as far as size of battery. If your a heavy user of trolling motor,,then go bigger,,,some manufacturers only make 20, 30, 50, 100, and 125 amp. Some make 60 amp and 80 amp. Some make 60, 80, 100, and 125 amp starting batteries also. I think Battle Born and Ionic also make a lithium battery that has a built in heater for the guys that fish in below freezing temps. There a bunch of combinations. Also,,check out bbc forum in their Electronics/Trolling Motor forum section..and go back a few pages scouting to the many different questions and answers on lithium batteries that users are asking. Electrical/Wiring/Trolling Motors

Here is the info I get from the phone app of a battery I brought in the house to use as a example for you to view.

Attachment 395167 Attachment 395168 Attachment 395169

Attachment 395170

Most lithium batteries depending on the cells used to make them are larger by 2-4 amp when purchased. For example,,this 20 amp battery actually is a 22 amp battery as each cell used in making the battery is equal size and will end up being alittle more than advertised size.

Cevans this is awesome information and thank you. I am very mechanically minded and can figure out most anything unless it has to do with electrical or computerized. So a lot of what you were saying has to be way dumbed down for me as we are once again talking about amps, volts. I tell folks I grew up with a family of carpenters and millwrights, welders and mechanics. So reading blueprints and diagrams not a problem. But reading an electrical diagram just as well be in Chinese. Makes no sense to me. In short I need help but would really like to move my boat over to something better than traditional batteries. One question how long to these batteries last verse traditional ones.


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From studying some of these different batteries, most have a charging cycle of 3000 to 5000 cycles. A cycle is charging the battery from 0 total dead to 100% fully charged. If your battery has been 35% used,,,that is only 1/3 of a cycle. If you look at my phone app. That 20 amp battery has been charged a total of 2 cycles as it’s only 6 months old and slightly used. How many times will you fully charge a lithium battery in a year of fishing? One thing everybody warns users is not to take these lithium battery’s down to 10% or completely dead,,and during winter storage, store them with about 40 to 60% fully charged. It protects the life of the batteries. A couple of manufacturers say it’s ok to store your batteries long term at 100%. Warrranty on a lot of these batteries are around 5 yrs. mIonic just bumped theirs up to 8 yrs. Battle Born is 10 yrs. I think my Ionics will be around a lot longer than me at 71. There is a few guys on BBC Forum that are in their 7th year usage of the same batteries. They sell and upgrade their boats, but keep the same batteries when switching to new boats. There is one guy in MInnesota that stored his lithium batteries at 45% charged all winter outside frozen for 6 months, Ionics! Each month he would go outside with the phone app and measure the amps available in his 3 lithiums, and only lost 1 amp in storage of cold weather depleting the energy out of those batteries where as, our wet cell and AGM’s loose a lot of amperage when stored for winter storage. How long will they last? I don’t think we have heard or found a answer out yet and it’s going to be a few years before we have a answer to that question. I do know as you use lithiums just like wet cells and AGM’s. As they get older with usage..if the lithium eventually only produces or charges to say, 80% due to age..the amps they provide even at 80% are the same if they were at 100% brand new. As your wet cell ages,,you get less power,,your run time decreases, they become charged quicker as the cells are weaker..and you then decide you need new batteries. Only way to know with a lithium drill battery is when it quits taking a charge then it’s time to buy a new drill battery. I guess same will be said with lithium 12 volt batteries.

The phone app also tells me, my batteries are 100% efficient so I think when the battery ages,,so will that percentage slightly drop.

Here is a really interesting 20 minute video on amp usage of batteries. It’s about amp usage and what your battery may provide.

How Battery Manufacturers Rating Standards Mislead Consumers - YouTube

Something else I didn’t know. When using a lithium battery as a starting battery. Make sure the battery you buy has a BMS build in it for starting motors. Check with all these manufacturers as a couple new ones don’t have it and are in the process of testing and building a BMS for a starting lithium battery. I think Amped as a 60 amp starting battery. Battle Born and Ionic has couple as a example 100 amp and 125 amp sizes. So shop around. Here is a interesting quote from Ionic on how low a starting lithium works.

the 100ah and the 125ah now have the same BMS allowing it to start the bigger motors and be charged by high amp charging systems without issues with voltage spikes
the starting capacity would not be affected until the 100ah reached a very low percentage but I have seen them easily start a 250 at 20%

IONIC LITHIUM BATTERIES . We carry all Brands of Trolling Motors and Graphs, Minnkota, Lowrance, Garmin, Motorguide
910-722-0001 call or text
info@drewcraft.com

Hate to ask dumb question and may have missed it. What is a BMS?


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Originally Posted by silverroach

Hate to ask dumb question and may have missed it. What is a BMS?


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Battery management system , I think


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Yep..the BMS works as a safety feature. It equals out the amps to all the cells inside used when 2 or more batteries are hooked together in delivering a charge. It prevents a fire if the battery overheats it will shut down. Same if the charge is too many amps in charging it will temporary shut it down. Same for overcharging the cells it will temporary shut down. If you were to tear the top of the battery off, it’s on the very top of all the cells with the positive and negative terminal wired to it then wired to the cell blocks inside.

Don't know if this has been posted here before. Cutting open a lithium battery case...
Signature Solar Cutting Open a Lithium LiFePo4 12V GYLL Battery - 4 Welded Cells - YouTube

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