Deep cycle battery, continuous load

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ZoomieFan
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Deep cycle battery, continuous load

I’m looking for a formula or table showing the safe continuous load of a deep cycle battery.

Using a simple formula a 120Ah car battery can supply 12A for 10 hours. Besides that totally draining a battery is a very bad idea, the 120Ah seems to be rated when using a 3.5A load. (for regular car battery)
So you can’t expect the battery to output 120A for an hour.
But what can I expect? That’s my question…

If the information I’ve found is correct a deep cycle battery can be depleted by 50-80% (20-50% left) depending on the type.

So… how long can 100Ah, 12v battery safely power a 300, 400, 500, 600 Watt load?

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

The Last Katun
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I think it’s an assessment, not a hard calculation; you have to think that the battery starts charged at just over 13.6 volts, and with a load of 600 Watts will absorb about 44Ah, but not for long; will soon be around 10 Volts and then the absorption (for the same consumption) will be 60Ah. It then depends on the operating temperature and other factors. It depends on what parameters you want to keep as stable as possible; do you care more about consumption? Absorption? The voltage? Or the exercise time?

ZoomieFan
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I didn’t consider the voltage drop.
I’m thinking about a simple load load that doesn’t boost voltage. So let’s say a 600 Watt lamp or 600 Watt heater.
That would means the watts drop as voltage drops because resistance stays the same.
A 600W, 12v heater has a fixed resistance of 0.24 ohm.
At 10 volts that 600w heater would output 417 Watt.

So to answer your question what’s most important for me: Watt, because that determines how fast the heater heats. That’s the only thing that really counts.
So starting with 600Watt and allowing to drop to 400Watt how long would the battery last?

But still I need some formula or table. Reason, besides the power output I also want to consider the total reasonable heat.
Allow me to clarify:
A 100 Watt load runs for 10 hours = 1000Wh heat.
A 1000 Wat load runs for 0.5 hours = 500Wh heat.
Those numbers are just for explanations and most likely totally false. Simply because I have no idea what they are. That’s what I try to figure out.

Another way of phrasing my question.
What do I need to boil a gallon of water?
Yeah, a battery bank from a Tesla will do the job, but frankly speaking I’m looking for a cheaper and smaller setup Smile

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

okwchin
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I think there are many factors that affect your calculation, and significantly enough to make the information very misleading or dangerous. That’s probably why there isn’t a simple look up table that summarises it accurately.

The many factors and variables will affect the results very significantly, particularly at the extremes of extrapolation.
- Battery chemistry is probably your biggest factor here, and a deep cycle lead acid will get Vastly different results to a ‘deep cycle’ lithium battery, and the big tip here is the batteries internal resistance.

If your using a lead acid battery, they all generally have a high internal resistance. That means that if you pull too much current, you get a significant voltage drop. This affects your load, and also affects your efficiency as more energy will be lost within the battery itself as heat (not to mention damaging the battery)

Lead acid batteries have a reasonable capacity, but it cannot provide it rapidly. I think the fastest recommended discharge rate was around the 0.2C mark, meaning you can discharge at 1/5 of its capacity, or drain it in 5 hours (a 100Ah battery can be discharged at 20A). At that rate you will be starting to lose increasing amounts of power to inefficiency.

For a lithium cell however, 1C discharges are the becoming the comfortable norm (100Ah can be discharged at 100A). Lithium cells in comparison have a Significantly lower internal resistance, so the speed of discharge is not going to affect your output of power anywhere near as much. Whether you discharge it slowly, or much more quickly, its going to give you a almost all of its energy, and lose little to heat. It would also mean minimal voltage sag.

In short, I think the max continuous discharge for a lead acid is around the 1/5C mark? I don’t know but thats what I recall. Is this what your looking for?

"like everyone else - I’m looking for my next “last” flashlight" -  ohnonothimagain

ZoomieFan
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okwchin wrote:

In short, I think the max continuous discharge for a lead acid is around the 1/5C mark? I don’t know but that’s what I recall. Is this what your looking for?
That’s certainly a good starting point. I’m not expecting 5 digit accuracy Smile

So for a 100Ah battery that’s 200 Watt load (rounding down because there will be all sort of losses)

Drain a 100Ah battery to 50% makes 50Ah
40Ah compensating for things like age. 480 Wh
200 Watt load at at 1/5C (also rounded down, to avoid unrealistic numbers)
Conclusion: a 100Ah battery can power a 200Watt heater for 2.4 hour.

As you wrote chemistry matters, but I’ve read the Ah of regular car battery is rated at 3.5A drain.
So at 1/5C, 20 Amps, the capacity likely is lower.

okwchin wrote:
For a lithium cell however, 1C discharges are the becoming the comfortable norm
That’s very useful info for me!
Any info on advised maximum discharge percentage?
Lithum batteries are much more expensive than lead acid, when comparing the same capacity. But if I can safely drain 30% more from a lithium battery it suddenly became 30% cheaper for practical uses.

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

okwchin
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Discharge percentages for lithium should be much deeper than lead-acid too, probably safe down to 20-30% I think. Possibly lower but I don’t personally like doing deeper discharge than that if avoidable.

Need to read up on what the safe discharge depth is for lithium, perhaps it is better than that.
Lead acid was always the cheaper option, but in your case, lithium might be competitive, especially if your outside the performance envelope of lead acid. Cell cycle life and degradation is also going to be your killer at the end of the day and if its cycled repeatedly then you will either need to provision for that in added capacity, or with $ for replacement.

"like everyone else - I’m looking for my next “last” flashlight" -  ohnonothimagain

ZoomieFan
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20-30% would be great.

Great article (taken from a masters thesis) based on cell cycles: https://www.powerstream.com/car-battery-for-solar-systems.htm

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

okwchin
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Thats a cool graph showing the battery capacity degradation! 20% drop by 7 cycles!

"like everyone else - I’m looking for my next “last” flashlight" -  ohnonothimagain

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I’ve been trying to work out the same (i offered to help a friend spec an off-grid system to continuously power a 120w heater on an allotment during winter which is proving way more difficult than i anticipated!).

While not a comprehensive answer 2 things you need to take into consideration are how much you want to sacrifice the life of the battery, and temperature.
Have a read through here: https://batteryuniversity.com/learn/article/lead_based_batteries but some key info is a table half-way down that states:

Depth of discharge Starter battery Deep-cycle battery
100% 12–15 cycles 150–200 cycles
50% 100–120 cycles 400–500 cycles
30% 130–150 cycles 1,000 and more cycles

and:

“The optimum operating temperature for a VRLA battery is 25°C (77°F); every 8°C (15°F) rise above this temperature threshold cuts battery life in half. ( See BU-806a: How Heat and Loading affect Battery Life ) Lead acid batteries are rated at a 5-hour (0.2C) and 20-hour (0.05C) discharge rate. The battery performs best when discharged slowly; the capacity readings are substantially higher at a slower discharge than at the 1C-rate.”

And i can’t remember where i pulled this from so you’ll have to verify it from your own sources but:

“The amp hours rating that batteries have is based on the temperature being 25 degrees Celsius and with every degree drop, there is a drop in the performance by 1%.
For instance, if you have an 110ah battery, but the temperature is 15 degrees Celsius, it will be performing like a 100ah battery.”

Marc E
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Ah cool, you posted a great link while i was trying to work out how to format that table Big Smile

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Marc E wrote:
While not a comprehensive answer
For me the table is a real eye opener.
I already knew a starter battery shouldn’t be drained below 50%, but I didn’t know even then it’s very bad (115 cycles)
Not even at a 30% discharges it can’t be used to power something on daily bases. It will be totally dead in a few months and long before that most likely the capacity dropped to unusable.

The deep-cycle batteries are a bit disappointing too. At 50% it likely lasts a year for practical uses.

Taking middle ground at 50% a deep cycle battery lasts 4x longer. Looking at it that way the deep cycle may turn out cheaper than a regular battery because you need to buy 4 of them during the deep cycle battery’s life.
Deep cycle also wins hands down on max advisable discharging amps.

Any data on the best charging amps?

This turns out to be quite a study. I’ve read about car, marine, RV and traction batteries.
Then there are the more expensive 6v batteries and the ultra expensive 2v batteries.

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

ZoomieFan
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Marc E wrote:

“The optimum operating temperature for a VRLA battery is 25°C (77°F); every 8°C (15°F) rise above this temperature threshold cuts battery life in half.
Likely something similar with temperature drops. IIRC Tesla cars even heat their own battery pack in the winter. So by heating the battery with power from that same battery the range of the car increases. That might be something you might have to figure into your equation. Spend 100Wh to gain 200Wh. Something like that…

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

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Very informative thread!
But now I have to ask, ZoomieFan, is using resistive heating as the load purely a placeholder or is it the intended purpose of this exercise?

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Username taken wrote:
Very informative thread!
But now I have to ask, ZoomieFan, is using resistive heating as the load purely a placeholder or is it the intended purpose of this exercise?

The primary purpose.

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

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To heat a space for comfort during a power outage?
I don’t know your circumstances but you might be much better off investing your space and money elsewhere.
As we’ve already established one battery can put out about 200W continuously, which comes out to about 680BTU.
For reference, a tealight puts out around 100BTU, a 1500W space heater (standard max wattage in North America) 5000BTU. And In my experience you really want those 5000BTU to heat a small room or keep a medium sized room tepid.
Obviously heat retention of your domicile and outside temp are major variables here.
So let’s say we go with 1000W or 3600BTU, the minimum I can see making a worthwhile difference. That’s 5 batteries already. And they’ll last you 2.4hrs. You want heat for, say, 12hrs. Thats 25 Batteries!

Again, I don’t know your circumstances, but if you live in a house with a furnace, buy a small (~1.5kw) generator and keep your furnace running. Buy an inverter generator if you have a newer, high efficiency gas furnace.
If you heat electrically or you’re worried about the gas grid going down, get a big (5-7.5kw) generator and run regular space heaters.

I can’t condone burning fuel inside (propane or kerosene heaters) but even that, with ventilation and a CO detector (battery powered obv.) might be an option for some.

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The purpose isn’t space heating but powering small stuff like a rice cooker, those immersion heaters, charging my phone, etc.
It’s also a hobby project to learn something new. Besides being flashaholics we are also battery-geeks Smile

For heating I would suggest to look at heated vests. It’s amazing how much heat you can get out a power bank.

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

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Get rid of lead acid headaches and go LiFePO4. It features excellent life cycle and can be discharged “down to the bottom” or fully cycled without damage to the batteries (LiFePO4 cut-off: 2V/cell). They're a direct replacement for lead acid batteries as the nominal voltage of 2 LiFePO4 cells in series is about the same as 3 lead acid cells in series, while their overall slightly higher voltage, lower resistance and super flat discharge curve means stable output voltage and solid power delivery. Power Long Battery, for example, manufactures some incredible small LiFePO4 cells; check Vapcell IFR26650 2600mAh (Red) @ review lygte-info.dk, that is this Power Long Battery cell rewrapped.

The chinese market, though, has some big cells from other manufacturers who seem good for stationary builds. Check this custom LiFePO4 search in AliExpress. As you can see, it is possible to get some pretty big battery banks for relatively affordable money. 

The human mind, and its programming, is at the forefront of a particular battle of The Light vs evil dark forces. Nearly every human being on this beautiful planet “Earth” has some sort of negative mind programming in its mind. And you better take care of your mind programming, or someone else will in this wicked world.

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Barkuti is right. Unfortunately the buy-in price is quite high.
Take a look at this guys channel. He is quite informative about battery power sources.
https://www.youtube.com/c/WillProwse/videos
He reviews stuff other than solar. Scroll down to look at home builds and commercial units.
All the Best
Jeff

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@Barkuti Very interesting. I only new about LiFePO packs that fit in the palm of my hand…

@jeff51 I’m still have to draw a firm conclusion, but the price of LiFePO can’t be simply compared to lead-acid.
A lead-acid battery must not be discharged more than 50%. So I can only use 50Ah of a 100Ah battery.
For a LiFePO that’s 80Ah of 100Ah.
That means in (my) practical use, I should compare prices of 100Ah lead-acid with a 62Ah LiFePO.
Did a very quick search and looking at it that way a LiFePO4 costs 10% extra. Shipping is a much bigger issue.

If want to draw 50A a 250Ah lead-acid battery is advised. Or 50Ah LiFePO.

Only 4kg for 55Ah, 12v LiFePO pack?
The claimed charging current is all over the place 3A…34A

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

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What sort of budget are you looking at?
For USB charging, I made a 4S 18650 pack going into a couple of marine QC-3 USB adapters.
Amazon USB QC-3

To recharge, I pull the batteries from the holder and pop in a new set. I use an external charger to avoid having to mess with a BMS.
These work off Lead-Acid just fine too.

What are you going to be using for DC to 120v AC? I use old UPSs for that sort of thing and have powered then with various batteries.
That guy I mentioned did a build for about $600 that is 280AH with a discharge rate of 250A. For about $600. Good for several thousand cycles.

All the Best,
Jeff

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jeff51 wrote:
What sort of budget are you looking at?
I’ve no budget. No that’s doesn’t mean I’ve an unlimited budget. Far from Smile
I’ve a target and then decide the price is right for what I get.
Less weight for the same usable capacity is something I would pay extra for.
Possibly I’m going to recharge using a simple solar panel. When I do I want to take full advantage of the sun when available. I don’t really care if recharge takes 10 hours, but still I want it much faster in case it gets cloudy. For lead-acid the adviced charging amps are C/10. For LifePO the numbers I found vary to much to be of any use. Anyway, if LifePO can recharge at a much higher speed, that would be something I would pay extra for.

My target is quite modest. 500 Wh would be very good, but half is acceptable.

This is also a learning experience. If I know the ins and outs of a small setup, it’s quite easy to upgrade.

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

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As far as I know even the shittiest LiFePO4 battery can be charged pretty fast: at 1C rate I'd bet. In fact, speaking of LiFePO4 I don't see a reason not to try even higher rates, at least for decent quality cells.

Only 500Wh, ZoomieFan?

If you are willing to solder, spot weld cells or just order a pre-assembled battery, take a look at this 26700 cell: LiitoKala 26700 4000mAh Lii-40E (Orange) -in fact, now that I recall I paid for these cells to get reviewed at lygte-info.dk LoL-. This cell is also made by Power Long Battery (can't say 100% sure, but considering that the flat-top geometry of cells is like a fingerprint, that is the reason I say such a thing; it also is a pretty good cell, while PLB is probably the most reputable cell manufacturer in China… the numbers match).

The cell delivered above 13Wh at 1C discharge, and pretty close to that even at much higher rates. Even if you consider a little bit less energy density per cell to “stay on the safe side”, for 500Wh the price of a pack can be very affordable. Take a look here at this LiFePO4 26700 custom search. Out of it: https://www.aliexpress.com/item/1005001556693880.html Under $50 for a 20-pack to USA or Netherlands, shipping included. They also sell many other big battery cells, and so you may be able to order some special request like a preassembled 8S6P (12V) or 4S12P (24V) battery. With 48 cells, the pack would yield above 600Wh guaranteed.

The human mind, and its programming, is at the forefront of a particular battle of The Light vs evil dark forces. Nearly every human being on this beautiful planet “Earth” has some sort of negative mind programming in its mind. And you better take care of your mind programming, or someone else will in this wicked world.

Please avoid fully quoting lenghty posts, namely with nested quotes. Trim quotes down to the essential. Helps with neatness and legibility. Thanks.

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Barkuti,
I’ve been considering 18650’s and 21700’s.
But how am I going to charge them?
That same question applies to the LiFePO4 batteries. I assume ordinary car battery chargers won’t work.
And even if they do, high amp chargers are quite ‘rare’. The most certainly exist but most seem to be around the 5-10Amp mark.
HJK suggests 2A charging for the orange cells. That 0.5C, not very high. But the 4C discharge is very nice.

That $50 will turn out a bit higher…
Above e22, 21% tax is added. Plus a e15 processing fee.
If I really pay that depends what the Chinese shop puts on the package. Quite often it’s hardly half of what I paid. Perhaps it’s the price they paid to the factory.
I could order them when in the USA. But lockdown…

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

ZoomieFan
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Barkuti wrote:

If you are willing to solder, spot weld cells or just order a pre-assembled battery, take a look at this 26700 cell….


Or instead of that a 33140. Might even be nice for a big flashlight Smile (if of decent quality)

https://www.aliexpress.com/item/1005001861008371.html

Chargers: 1xBasen BD01 5/5, 1x Gyrfalcon All-88 4/5, LiitoKala: 3x100 3/5, 2x202 3/5, 1x402 3/5., MiBoxer C4-12 3/5.
Flashlights: DQG Tiny III 26650 5/5, FiTorch MR35 3/5, Haikelite SC26 HD 3/5, Lumintop Tool AA/AAA 4/5, Nitecore LA10, Sofirn C01 BLF 3200k/5600k 2/5, Zebralight H600Fc 3/5.
Powerbanks: EasyAcc 26800 mAh 3/5, Xtar PB2 4/5, Xtar PB2S 5/5
Waiting for: (DQG Tiny) 21700 EDCs.

jeff51
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Location: Middle of Texas

Absolutely don’t let a car battery charger in the same zip-code as a lithium battery. Unless you like fire.
A completely different set of charging parameters is used for Lithium batteries.

Some lithium battery packs are designed with BMS built in so that they can be used with conventional chargering applications. The Battle Born batteries come to mind that can be used as a direct replacement for many lead cell applications. Bring the big checkbook.

Anytime you put cells in series and expect to charge them without separating them, you will need a BMS.
A Battery Management System. This is a device that equalizes the charge across the pack so that poorer cells will not get pulled down after multiple charge – discharge cycles.

This is what typically happens in older NiCd power tool packs. Eventually one or more of the batteries actually reverses polarity and needs replacement.

Modern packs (should) have a BMS to prevent over discharge, overcharge, and keep the cells equalized.
It’s the red thing in the video in my previous post.
All the Best,
Jeff