Extending life of old polymer Li-Ion battery

[13hm13]

For the sake of experimentation, I'm interested in extending the life of an 8-year-old 7.4v Li-Po battery from a portable DAP (digital audio player).

The DAP is a Chinese Teclast t51 (aka: Nationite s-flo2), manuf. approx. late 2010. See images below (battery is green-colored in top photo. Note: that the stock batt. is two 3.7v cells in series=7.4v total)

The DAP unit has been in almost daily use for the past 7.5 yrs. Never replaced the battery. So it may come as no surprise that the batt. is starting to go.

For about a year, the battery has lost capacity. Currently, I can get no more than 0.5hrs of play time. Maybe 1hr on very warm days.

What can I try to do to the orig. battery to recover some life?
(I say Dave's video on dropping batts. So I tried very gently twisting the pack 2-3 degrees on both axis. I have also compressed very gently with with my finger/thumb. Made no difference in performance.)

(BTW: I am planning on replacing the battery (I think this is the battery): http://www.batteryspace.com/polymerli-ionbatterymodule37v2500mah925wh-prewiredwithpcbic.aspx. Extending the life of the orig., as noted, is for the sake of experiment only!)

[Audioguru]

If a lithium rechargeable battery is discharged too low a few times then its capacity is reduced.
If it is fully charged most of the time then its capacity is reduced.
You are lucky that it lasted more than 3 years.

[Daixiwen]

You could check if the two cells are still balanced. If not, rebalancing them could make the battery regain some capacity.

[13hm13]

You could check if the two cells are still balanced. If not, rebalancing them could make the battery regain some capacity.

I have heard of this but I have no idea how to approach re-balancing cells. Please give some advice--THX!! (I'll try to Google the topic in the meantime).

BTW: The stock batt. that the Teclast DAP came with is almost impossible to find because of its dimensions and voltage: 85x55x3mm at 7.4v

BTW2: I have another Chinese DAP (made by Colorfly) similar to the Teclast unit. The battery dimensions are the same but this is single cell which outputs 3.7v. That Colorfly DAP is almost as old as the Teclast DAP, used almost as much, but the batt. seems to have not degraded.

BTW3: A Cowon DAP (purch'd 2006) is also going strong (with orig. battery).

[FotatoPotato]

Hey 13hm13, Unfortunately there isn't much you can do to prevent the "decay" of a lipo/ lion battery after it has been in use for so long. All of these batteries have a certain number of charge/ discharge cycles that they can go through before they wear out and stop holding a charge. The reason being is that over time the internals of the battery naturally decay and thus the capacity lowers too. The best you can do is to either buy some new batteries with the same rating as the ones in the DAP or just to get a new one.

Oh and PS: DON'T TWIST OR SQUEEZE OLD LIPO BATTERIES  Over time the lithium electrode will grow small crystals (Dendrites) due to over discharge, long storage periods and over charges that move towards the Anode and if you twist the battery and those dendrites touch... well I think you know what will happen. The same goes for squeezing or pressing on the cell's. Soooo I would probably not do it with such an old cell or you might just get a surprise fireworks show.

[brainwash]

You cannot restore LiPo cells at all, you can only bring some of the shorted ones from the dead.
You can rarely restore lead-acid ones.

I've tried all the magical potions for all the chemistries. I'd put my success rate at 5%, if that.

Best bet is to replace it with a battery that fits, even if it's smaller capacity. And drop/twist/punch them, they really don't like that, expect to be punched back.

[Daixiwen]

To find out if they are unbalanced, measure their open circuit voltage, preferably when the battery is almost discharged or almost charged. This is where the voltage difference between the cells will be the highest.
If there is a significant difference, there are some chargers that can rebalance them automatically, or alternatively you can connect them in parallel through a resistor and leave them overnight.

But that said don't expect miracles, on a 3 year old battery you may regain some capacity if the cells were very unbalanced, but there is probably already a relatively important capacity loss on each cell themselves.

[13hm13]

But that said don't expect miracles, on a 3 year old battery you may regain some capacity if the cells were very unbalanced, but there is probably already a relatively important capacity loss on each cell themselves.

This batt. (orig, stock Teclast) is almost 8yrs old, with probably over 2000 chg. cycles.

From its dimensions, the stock batt. (see image in OP) is roughly two iPhone 5 cells in series.

A better look at the battery inside the Teclast DAP:

[brainwash]

8 years and 2000 cycles (if true) is outstanding for a LiPo battery, not to mention the fact it's in an "offshore" unit. I don't think any battery I've used lasted more than 1000 cycles without an unusable capacity (or IR) drop. My brand-name ones degrade significantly at around 400 cycles, the offshore ones barely last 200.

[CatalinaWOW]

Balancing is the only chance of any added life for this battery.  Which will require opening up the battery to access internal connections.  Something which can be done, but requires extreme care and involves a level of hazard that many are not comfortable with.  Some batteries have external balancing leads but there is no sign of this in the picture.

If you do choose to open the battery up, take extreme care not to puncture, tear or stress either of the cells.  Concentrate on the end where the connections are - at the right of the picture you published.  Also take great care not to short anything inside.  The battery may be dead enough to not cause massive sparks or heating, but maybe not, and any short is likely to remove any remaining life these batteries have.

It should not be too difficult to make a replacement battery.  Just search by size for single cell batteries of the same physical size or smaller than the existing cells and hook them in series.  Technology has advanced enough since your original battery was built that the cells should be at least the capacity of your originals.  Ideally you should buy a large quantity of cells, measure the capacity carefully and select two that are very closely matched.  In these batteries without balance provisions that is the only way to achieve (relatively) long life.  Since you probably don't want to do that you can just arrange to have relatively easy access to the terminal connecting these batteries in series and plan on rebalancing it periodically.

[13hm13]

Good feedback from all. Thx.

The two-cell stock batt. is a bit of mystery.

The numbers/code printed on the exterior (see photo) could not be traced down via Google.
So I'm not sure about the all-important mAh (capacity) spec.

It's spatial dimensions are: 86mm x 56mm x 4.5mm. (So, each 3.7v cell is 4.5mm thick, but 86mm x 28mm)
As noted, there are two cells in series. I have not dissembled the batt. so I don't know if there is mini protection (or balancer) PCB in the battery pkg.
 
A modder/hacker (of DAPs) on a Russian electronics DIY forum noted this:

http://player.ru/showthread.php?t=119826

"...replacing the drain battery for an assembly of two LP473850 1090mAh, installing a balancer for equalizing the voltage between the banks" [sorry! Google translate not so great!]

I Googled "LP473850" and found a Chinese company that (more or less) has them:
http://www.lipolbattery.com/lithium%20polymer%20battery.html
The Russian modder's project was from late 2012. So the cell specs have changes a bit. Notably, capacity is now 1500mAh.
I have no idea what the DAP's internal charge circuit can safely deliver?

[13hm13]

8 years and 2000 cycles (if true) is outstanding for a LiPo battery, not to mention the fact it's in an "offshore" unit. I don't think any battery I've used lasted more than 1000 cycles without an unusable capacity (or IR) drop. My brand-name ones degrade significantly at around 400 cycles, the offshore ones barely last 200.

2000 cycles is great, but not anything stellar.

As noted in one of my posts above, I have a couple of Chinese or Korean DAPs that are at least 8 years old, with similar cycles. And they are all going strong with orig. batts.
There are some low-end Chinese brands (or models) that may not be so durable.
But I usually go for the mid-priced 'audiophile' units that are normally of higher build quality (like better Chinese test equip., such as Siglent).

I did have a 3.7v li-po puff up (and degrade a little) on a Cowon iAudio DAP (high-end Korean brand, made in 2006). But that was after 4 years of 2hrs/day, use! Its battery was made by Samsung, I think.

[brainwash]

2000 cycles is great, but not anything stellar. Most cells rate 300 cycles for liability reasons, and that's 300 FULL cycles. If the charger charges only to 90% and the device cuts off at 20%, lifetime can be extended to well beyond 1000 cycles.
Cycle lifetime is also highly dependent on chemistry. Those high capacity chemistry cells (4.35V cells) may only last 300 cycles, but those standard cells can easily last 1000 cycles to 70% capacity.
Some high endurance Li-ion cells (particularly LiFePO4) can do 10k cycles and still retain 85%+ of capacity.

If your cell only lasts 200 cycles, either you are buying the cheapest AliExpress special discount ones, or you are not charging it correctly.
Around half Shenzhen taxi run on Li-ion batteries (BYD F0 EV), and they run 24 hours per day, 2 drivers shift. If they only last 200~300 cycles, they will end up losing money.

Just one example: my laptop's battery (Lenovo, mid-high range) is down from 62Wh to 24Wh after 402 cycles and 5 years. Bought a cheap replacement one (with warranty), it's down from 76Wh to 62Wh after 4 cycles of "settling in".
I'm talking full cycles always, but I tend to protect my batteries and set a charge limit, avoid full discharge and heat. 400 cycles for me has been the norm, rather than the exception.
I'd love to know how to identify good battery packs, it would save me some frustration.

[13hm13]

What about those protection PCBs that are sometimes attached to batts.?
I think they are required by law -- correct me if I'm wrong. May depend on which country/region you're in.
For the Teclast DAP, I'm not sure the stock batt. has one (or two -- one per cell). I haven't disassembled the batt. yet.