NH-14WM Ni-MH anomalies

I have a couple of MZ-R55 mini disc Walkman that I had virtually abandoned due to the failure of Sony OEM gumstick batteries to power the units for more than 10 minutes from a full recharge. The same battery will run the DD9 for around 2 hours but put it the MZ-R55 and up comes the "Low Batt" flashing display and the Walkman shuts down. Even an expensive new Sony battery in shrink wrap gives the same result.
However, an older battery, in the black and orange design will run the same MD player for 2 hours after a full recharge.
So can anybody explain why some of the same OEM batteries appear to better than others and how do you find a good one?. I have 5 batteries. They all work in a cassette Walkman but only one will run the MZ-R55.
Cheers

 

I do not have the answer... but my own experience is exactly the same! Out of a dozen old Panasonic/Sony gumsticks 50% were dead and the rest worked fine. Out of about a dozen new generic (Chinese, in blue-color off eBay) half were DOA, another half lasted at 50% of the old Panasonics... Never bought any "expensive new Sony battery in shrink wrap" but those must be NOS from the olden days?
We need a professional help from @Mister X, myguess, to figure when the last "brand-name" gumsticks were produced

 

Thanks for the info on the batteries. Definitely you notice the charging cycle seems shorter on the batteries that will not power the MD Walkman. It seems to make no difference though if you run them out completely in a cassette Walkman which will run for several hours after the MD display comes up with Low Batt and the Walkman shuts down. I'm certainly going to make sure the one good one I have is discharged fully before recharging it. BTW they all get hot in the charger but I suspect the 100% drops to 60% on some as described in the thread from MisterX.

 

Wow. The MZ-R55 has been on repeat play for 3 hours on the good Sony OEM NH-14WM battery. So charging it in the old 110VAC external Sony charger and not inside the MD Walkman has something to do with maintaining the charge in the battery. They're not supposed to have memory effect but something happens to reset them so they end up with less and less capacity after each discharge until it gets to a point where the MD auto detects low battery but a DD9 or any other gumstick powered cassette Walkman runs on this supposedly flat battery. I used to think it was a fault in the MD or poor contacts in the MD during charging and it still maybe even though both behave the same way. I just wish you could get a Lithium ION version of the NH-14WM like a LI-14WM.
My MZ-R30 has a Li ION battery that is 20 years old and it's still perfect.

 

You are really lucky with that. Recently I was trying to get a new battery for my wife's Sony phone which is probably about 15 years old.
I bought a new old stock Sony one and it wouldn't charge. The seller kindly sent me two more. Neither of those would charge.
I ended up buying a cheap Chinese copy which does at least work.

Not quite as bad as two of my Sony MP3 Stick type players. Both were damaged by swelling L-Ion batteries. One hadn't been touched for five years which I think was the problem. I did manage to salvage enough parts from them and a battery from a £5 Ebay player to make one working one.

p.s L-Ion batteries are typically about 3.7V so a completely different voltage to a 1.2V gumstick.

 

It's still a mystery to me why some NH-14WM batteries are fine but others won't charge sufficiently to run the MD player. Even new out of the original packaging, Sony Japanese battery failed but the made in China Sony battery is good for 5 hours in the MZ-R55. I'm not going to bother with the eBay cheap alternatives. The feedback on some of those indicated people who bought them had issues with charging when trying to use them with MD players.
Again they all seem to run a DD9 or WM-WX1 wireless Walkman but the MD and I assume the Discman requires more power and unless the battery is at full spec it won't run these devices.

So my tips for keeping your battery in optimal condition are:

1. Never leave the battery in the device when not in use
2. Use the plastic case to store the battery between uses.
3. Dont charge the battery using the in built device charging button but use an external charger. Preferably the OEM one and not a cheapie.
4. Before recharging make sure the battery is fully discharged. When an MD says Low Batt you can still run other Walkman in this battery until it is fully discharged. Then recharge it.

Seems to work for me. 5 hours on a gumstick battery in an MD Walkman is pretty much as good as it gets and means not having to carry that external battery case with 2 double AA batteries around wih you.

 

It sounds like differences in internal resistance to me. A battery can have a large capacity but if the voltage drops when high current is required it won't power some equipment. Remember rechargable Alkalines? I was trying to use some in a battery case to power an 8mm camcorder. Even fully charged they couldn't do it.

A top of the range battery charger / analyser might tell you the difference between your batteries.