@inq I looked over the ad, but I don't see the dimensions.

7.5 cm/2.95 inch X 11.6cm/4.57 inch X 8.2cm/3.23 inch

Bill

Posted by: @greendragon

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Just to recap for everybody I was looking at this listing:

https://www.ebay.com/itm/166320027173

At the 18V 12AH Version (Choose for select box on ebay page)

The following is the title of the listing -

12Ah 6.0Ah Battery For Makita 18V Li-ion BL1860 BL1850 BL1830 Cordless Tool USA

Bill

Ok... I'm a little confused isn't this the one you're suggesting? 

OH!... I see... It's a bait and switch.  I hate ads like that... The picture shows the 12.0Ah battery (out of stock) but the selection (that you can't see) is the price for just the charger.  $45 sounds like the right price for 6.0 Ahr, 15x 18650's to get that kind of Whr.  Still might be a good deal... if the cells are good quality.  And that unit has to include the BMS and other safety electronics (I would hope).  Guess... you have to take the leap whether its as good as the Makita at twice the price.  If you could 3D print the receptacle in your bot to slide the battery in, that'd be pretty cool!

I must be blind, I still didn't see the dimensions for those units, but the dimensions you gave would easily hold 15x with room to spare.  You might double check the weight.  I think the cheap knock offs actually have fake cells (dimensions right, but less lithium guts).  @zander, didn't you mention something about that... that the weight of the cell is a semi-good gauge of expectations???  45 g/cell ===> 675 grams + plastic housing and support BMS/electronics call it 700 grams.  If it weighs 500 grams... walk away!  😆 

VBR,

Inq

@greendragon You have to click the slider buttons to get to the next few pics. BTW, that is NOT made by Makita and their ad copy photoshops the Makita names off the power tools displayed. Proceed with great caution!

@greendragon Check the price again, the 12AH is now out of stock.

@inq The dimensions are on the 3rd picture.

 $45 sounds like the right price for 6.0 Ahr, 15x 18650's

REALLY, the max for a 18650 is 

An 18650 battery is a rechargeable lithium-ion battery. They tend to have a nominal voltage of 3.6V and range in capacity from 1800mAh to 3600mAh.Mar 13, 2023

and for LiFePO4 (the safe one)

It's a fairly simple process to look up the energy density of a given Lithium chemistry. Then simple math will tell you that 18650 cell with mass of x can not possibly be 9000mAh (yes, I just saw one on a non foreign web site)

@inq BTW, that is NOT bait and switch. They are selling several similar products, different capacities, different voltages, with and without a charger. The 12Ah was available yesterday, but they just ran out of stock sometime today.

BTW2 for you and @greendragon here is the screen where you could not see the dimensions.

On the left is three pics vertically, the 3rd clearly shows dimensions, and clicking the > (next picture) twice shows you the full-screen dimensions. You both need to see an eye Dr, and I should start charging for this easy stuff. LOL, just kidding before some #^*) flames me.

Posted by: @zander

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BTW2 for you and @greendragon here is the screen where you could not see the dimensions.

@greendragon had found the dimensions and he was looking at the 6Ahr battery anyway.  I'm used to the dimensions being down in the "searchable" text description.  Didn't think to look in the secondary pictures.  Me... I'll stick with my free 18650 cells and being careful.  The batteries cost more than the rest of my entire bots... hardware/electronics/structure.

PSA

I was just checking my supply of 18650's and about 4 to 6 are showing up as dead and/or NiCad or NiMH.

I have a charger that identifies the chemistry (I am not 100% sure it works 100% of the time, though)

Do NOT trust Amazon, I will bet 100% of battery sellers are NOT Amazon but 3rd party folks.

A very popular and reliable site is 18650canada.ca. If you go there, a PSA will pop up (this is relatively new), warning that 18650Canada.com is NOT related and is getting many complaints. I'm not sure about shipping, especially since it's lithium, but at least your Yankee bucks will buy about $1.36 worth of Canadian goods.

@inq Ok, I thought he was looking at the 12Ah. The dimensions for the 6Ah should be different then.

I still think it's questionable at best, and I can buy the now 10 cells for a heck of a lot less, $60 and they have both charge and discharge protection built in. Also they are 5.2Ah capacity (5s2p), I already own a charger.

Hello All:

As always it seems everybody has a different opinion on how to do things, and that's good. I now have to decide what I want to do -

1. Use Lipos

2. Buy A power tool battery, and take my chances.

3. Use 189650 by buying them, or salvage them and build my own battery.

4. SCREAM, and RUN AWAY....

At the moment I am leaning toward option four.....

Bill

@greendragon How much room do you have for the battery, and is there any chance of enlarging it?

How many hours do you want to operate before recharging (I assume you will get two since the recharge time could be long)

Option 2&3 are the same.

I know where to get several physical sizes but will be either 12V or 6V and maybe only 25Ah or 12Ah.

Also what about building your own out of raw prismatic cells? Often done by DIYers, but requires more parts like nickel strips to weld the cells together, Kapton tape, of course a GOOD BMS.

@greendragon What country are you in?

@greendragon The best energy density is LiPo at 140-200+ Wh/Kg then comes the 3 different LiIon chemistries, LiLion (Cobalt) at 150-190 Wh/Kg, next best is LiIon (Manganese) at 100-135 Wh/Kg then LiIon (Phosphate) (?LiFePO4?) at 90-120 Wh/Kg (those number jive with my 7,200Wh battery bank. 

The big advantage of LiPo is volume and weight. They are typically packaged in some sort of plastic bag.

I think this will work, https://amz.run/7UOp . You only need 12V, some 6V (via a buck converter) and I think you mentioned one other lower voltage which again is a buck converter.

2 for $99 for 14.8V and 6.2Ah is a good price. MAKE SURE to buy a high quality LiPo charger (check RC forums and reviews, a fire bag or two (1 smaller inside a larger) and a stone to sit it all on.

This is the charger I have, https://amz.run/7UOt so far it works just fine. It is OOS but you should be able to find the same charger sold by other sellers on Amazon in your country.

@greendragon I did a quick look, you may want to spend more time looking at the RC sites. The top of the line looks like the iCharger at $500, then the SkyRC D200 NEO at $150 then one like mine https://amz.run/7UP4 for $74 CDN.

If you have not seen a Lithium fire, first go watch a YT video about that. It is no joke. When I charge, I have an emergency disconnect, and the battery and charger are inside a firebag inside a firebag all sitting on a fireproof surface. I only feel really safe when I can charge outdoors, but that is only for about 8 months of the year (I live in Canada but 2.5 degrees below the 49th parallel)

Hi Ron @zander,

RE: This is from a very reputable website.

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Lithium-based cells, however, don’t allow overcharging or over-depletion well and need protection from these conditions to achieve maximum life. These 18650 li-ion cells are protected against both of those problems by internal circuitry and also add short circuit protection for safer operation.

My Google of that quote led me to an Xtar advert, which described the cell as "18650 3.6V/3.7V LED Flashlight 2600mAh Button-Top Rechargeable Battery"

Apart from indicating its increased length, and the quote, there was no indication of the recommended usage in terms of current output, etc.  Inserting a circuit between the 'actual' cell and the external anode connection will change the characteristics of the whole device. How one is supposed to do a proper toleranced design that utilises these cells on this basis, I am not clear.

Pragmatically, I guess, if you only buy them for a single flashlight, then they either work or fail because the current drain exceeds the limit, although that does not allow for a device that works at room temperature, but then trips on cold, dark night, due to the component characteristics changing with temperature.

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Looking more closely at the quote, it says it has protection from:

• overcharging
• over-depletion
• short circuit protection

Considering each of these in turn, detecting the problem could be based upon:

• Overcharging indicated by cell voltage exceeding a certain value
• Over-depletion, presumably Over-discharging indicated by cell voltage below a certain value
• short-circuit protection is (massive) overcurrent, which could also by detected by cell voltage below a value, and/or voltage drop across FET(s) exceeding a certain value

For all of these cases, two FETs back-to-back, between the anode of the cell and the anode connection cap could provide the required isolation when any of the above states is detected. The fault detection requirements implies a rather simple two or three voltage comparator function.

This function, plus the MOSFETs, is roughly comparable with the DW01 and FETs I mentioned previously.

However, as the total function is required in vast numbers, even allowing for the fact that only a minority of 18650 cells include any protection, I presume it is available to the cell manufacturing trade as a kind of circular disc component with just three connections, namely the two 'raw' Li-ion cell outputs (anode and cathode) and the overall cell (anode) external output.

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I accept this provides a useful measure of protection, but I find regarding it as a BMS is a stretch of the imagination, and could lead to someone mistakenly thinking the device included more 'BMS-style' maintenance control than it did.

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As for the small cells which I suspected existed for mid-range power tools, and you found a reference to a design nominally 10 mm shorter than my wild guess, I suspect they are a version of the most common/well-established chemistry which uses cobalt as one of its 'ingredients' but is usually just referred to Li-ion. i.e. apart from being about half-size, half-capacity, etc., they are probably the same as their ubiquitous full-sized brothers.

https://en.wikipedia.org/wiki/Lithium_cobalt_oxide    for a description of most of the cells we see, (excluding the LiFePO4 type).

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Best wishes, Dave