9V NiMH Made in Greece Frankenstein - Mix of cells from 2013 and 2017

[Kiriakos GR]

I am presenting here test results of one example that this it should be avoided.

At 6/2012 I had purchase from eBay USA, 4x Tenergy Centura 9V NiMH, over the years these batteries they started collapsing, even if they had an easy life within several multimeter.
The problem was not endless recharge cycles, but rather their chemistry this was deteriorating.
The survivor of this batch, it suddenly stopped working this year, due several shorted cells.

Also back at 2017, I had purchase 4x TRONIC 9V from Lidl super market.
One of them melted and when softly injured, even with one cell electrically shorted, this battery it was not refuses to be charged.
But eventually this also collapsed this year.

TRONIC 9V this using very short barrel type of cells, Tenergy Centura this has identical construction, Tenergy Centura inner cells they have few mm smaller diameter.
The body of the TRONIC this accepted three or four, still alive 1.2V cells from the Tenergy.

I thought, better having a Frankenstein alive than two 9V batteries as permanently damaged.  

The good side of my Frankenstein,  this is a working battery but it can deliver only 87mAh.

Battery manufacturers, they write at safety advice's, never dissemble a battery. 
But there was no other way, so this experiment to happen.

My new high-end battery discharging system, this delivered interesting clues, of what happens within the battery.
97mAh this equals to  1H and 42 Minutes under 50mA load.
At first 1H 15 Minutes, the discharge curve appear almost normal.
Then most aged cells they start collapsing fast.
Eventually this poorly balanced battery pack with 9V output, this gets down to it knees. 
 
This experiment, it is a fresh experience for me that I decided to share it in public.
My Frankenstein this will serve again, within an analogue multimeter, this not be frequently used.

It is surprising that NiMH chemistry this might survive up to 13 years, if the battery this is manufactured with strict quality control.
Our new problem, we do not know whom at China mainland he skip this strict quality control, in favor of his own profitability.
 
TRONIC this is a dead branding today.
Tenergy Centura this is still available, but Tenergy never feel the responsibility to deliver a damn datasheet for them.

Frankenstein internal resistance = 10,19 Ohm at 1kHz 

[Andrew-88]

I think that a few more charge / discharge cycles, they might awake even the last bit of chemistry in this battery. 

 

[Kiriakos GR]

I think that a few more charge / discharge cycles, they might awake even the last bit of chemistry in this battery. 

I am starting too, at becoming a believer of this theory.
An 9V battery at electrical test and measurement tools, this is unable to be fully cycled as it does when this powering a microphone.

An 9V battery this has seven 1.2V cells inside, when you do perform discharge test, every single cell this recover and a bit more of it lost capacity.
If battery refresh program, this helping AA and AAA with three repeated tests, an never cycled 9V battery this require much more cycles, so this to fully wake up.

I have currently proofs, that a second time test, this deliver different capacity measurements,  different internal resistance, discharge curve even this improves. 
Therefore I will repeat cycling for at least five times, before I deliver an opinion of DUT actual health status.