Buy a new 18650 battery for my headlamp, I suspect the labeled capacity is bogus - Page 1
Forum section: electronics / general

author: ASICS
author_rank: Contributor
timestamp: June 13, 2024, 06:32:01 am
content: I recently bought a new 18650 battery that says 2000mAh on it.However, I am a bit skeptical about this as my headlamp turns off after a short period of use.I was advised to set the discharge cutoff voltage to 2.8V when testing the battery capacity. I will try this time. Wait for my news.

author: kripton2035
author_rank: Super Contributor
timestamp: June 13, 2024, 06:36:13 am
content: if you did not buy this from a reputable seller/brand, pretty sure you ended up with some knockoffyou can measure the real capacity with some dedicated device, but "usually" you can estimate it at half the marked capacity...

author: ASICS
author_rank: Contributor
timestamp: June 13, 2024, 06:37:14 am
content: [ Specified attachment is not available ]

author: ASICS
author_rank: Contributor
timestamp: June 13, 2024, 06:44:38 am
content: I didn't think about it that much and just bought one, which I shouldn't have done.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 13, 2024, 07:12:29 am
content: Quote from: ASICS on June 13, 2024, 06:32:01 amUsually it is lower than 2.8V, for example these LG datasheets specify 2.0V:https://www.dnkpower.com/wp-content/uploads/2022/11/LGINR18650-HB2.pdfNo matter the brand, consider it in practice to be 1.5...2 times smaller than what is written on the battery, and be happy with whatever it is. Either it is 1, or 2, or 3 Ah, that is still a lot for a LED flashlight. Other parameters (like battery lifetime) might be more important than the Ah.The measured capacity also varies with the discharging current, the temperature, etc. Usually the Ah on the batteries is not a lie, but the conditions in which those values were measured are unrealistic for day to day use of the battery. At a very low discharging current you might even get 2..3 times more Ah than specified on the battery.

author: tom66
author_rank: Super Contributor
timestamp: June 13, 2024, 01:19:27 pm
content: Quote from: RoGeorge on June 13, 2024, 07:12:29 amGenuine cells from the likes of Panasonic, Samsung, LG, ... should be at their nominal capacity from new. Not varying by 2x. If the cell is from a generic brand then all bets are off. Buy cheap, buy twice.

author: Peabody
author_rank: Super Contributor
timestamp: June 13, 2024, 02:13:30 pm
content: You're in the US, so you might consider getting a battery from Digikey. There was a guy from Tiny Circuits on The Amphour podcast who sells 18650 cells on Digikey for about $7. They are 2500mAH as I recall, flat top, unprotected. They've been at zero stock for a while, but of course Digikey sells other brands, and I think you could count on whatever you get there.Edit: I just checked, and apparently you can order them directly from tinycircuits.com at the same price, and they show as in stock. I don't know about shipping. And they are $1 cheaper at Mouser, which has stock.https://tinycircuits.com/products/16850-lithium-ion-polymer-battery-3-7v-2500mah-cylindrical-cell-work-in-progress

author: ASICS
author_rank: Contributor
timestamp: June 17, 2024, 03:48:44 am
content: Quote from: RoGeorge on June 13, 2024, 07:12:29 amIt is normal for batteries to have a shorter lifespan during use.However, the length of discharge time can greatly affect the experience of using the product. When you are often out and about with your headlamp, a sudden dead battery can leave you at a loss for words.The capacity labeled by the battery supplier does not match the actual, that is false advertising.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 17, 2024, 04:36:48 am
content: Due to popularity of e-cigs here it's almost impossible to get decent quality cylindrical cell. Local marketplaces are swamped with crappy cells advertised with inflated specs to hell and beyond. Reputable brands either gave up trying to compete with them, or jacked their price instead. Being lithium I can't just buy it from overseas either.I'll consider myself happy if those 2 bucks HyperFire 100000mAh 18650 cell actually get more than 1000mAh, hold charges, and hopefully not literally live up to its name.

author: Tation
author_rank: Regular Contributor
timestamp: June 17, 2024, 11:17:45 am
content: Last time I bought 18650 cells (Liitokala), their measured capacity were ±3 % from advertished (2200 mAh) when discharged at C/5~C/3.

author: SeanB
author_rank: Super Contributor
timestamp: June 17, 2024, 11:51:48 am
content: That cell looks like a recycled one, look to see if there are marks from removal of tabs, as they mostly come from old laptop packs, just get as new shrink sleeve and inflated capacity, and the only test is if they are above 1V, if at all.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 17, 2024, 12:04:45 pm
content: You'd be still kind of lucky if it's refurbished. Usually it's much smaller cell packaged inside the larger tube with sand for padding. You'll notice those cell to be much lighter than usual. Some do put scrap steel bar as ballast, but that'll also noticeable when the cell is not radially balanced.Here a forum post with the exact same thing:https://www.eevblog.com/forum/dodgy-technology/10ah-18650-cells

author: tom66
author_rank: Super Contributor
timestamp: June 17, 2024, 12:06:54 pm
content: The other problem is with 18650s they are not really designed to be used in products where they can be removed/reinserted, especially for the unprotected cells, as the cycling can wear the wrapper on the cell and lead to short circuits.This has led to manufacturers trying to control the sale of these batteries to consumers, leaving consumers to buy the shitty cells instead or source the premium Samsung, Panasonic, etc. cells from less honest places where counterfeits are more common.

author: SeanB
author_rank: Super Contributor
timestamp: June 17, 2024, 12:10:50 pm
content: Quote from: ArdWar on June 17, 2024, 12:04:45 pmRecycled cell with low capacity is sold as scrap steel price, so cheap. Just have to strip the spot welds off, put on a new sleeve, and sell it, after a cursory check on assembly if it had any charge, if not put in another, and put the dead into a charger for 5 minutes, and see if it works with next lamp.I got a lamp with these poor cells in it, and simply put in both a DW01 board, and a pair of used laptop cells that are guaranteed, because the charger took 24 hours to charge them, to have at least 5 times the capacity of the original *****Fire cells. Those are going as steel scrap soon.

author: wraper
author_rank: Unknown
timestamp: June 17, 2024, 01:22:58 pm
content: Quote from: RoGeorge on June 13, 2024, 07:12:29 amOnly if it's an absolute bottom of the barrel fake garbage and then you usually get even less capacity. Even relabeled used cells usually have more. What is guaranteed to be garbage are cells with capacity marking that is so high it cannot possibly be real.