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Is there any "smart" way to charge 8.4 V NiMh battery ?
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BravoV:
... or just charge them as dumb old way using slow and low constant current ?

As I'm aware, cmiiw, the peak detect just can be effective only in single cell charging, and if > 1 cells in series, it will not be reliable mechanism to terminate the charge.

Any thought ?

I am aware of 9V Lithium primary cell, its just just looking for 9V Alkaline alternative.

Random image of 8.4 V NiMh battery grabbed from Google.
Nusa:
https://www.google.com/search?q=nimh+smart+charger
BravoV:

--- Quote from: Nusa on March 10, 2020, 08:16:58 pm ---https://www.google.com/search?q=nimh+smart+charger

--- End quote ---

Thanks, but I guess u dont have any idea and understand what I am talking about.
magic:
 :popcorn:

I actually wondered about the same. I figured a slightly smarter solution than CC might be a 10V supply with limiting resistor. That's 1.43V per cell, which AFAIK is close to full capacity but not all the way there. It also charges empty batteries with higher current and then slows down to safe trickle charge.

By the way, that VARTA battery doesn't have rounded corners and it may not fit into some equipment. Guess how I know.

edit
That's exactly how I charge one oddball triple-cell battery. 5V in series with 220Ω. Chosen to meet two constraints: maximum rated fast charging current into empty battery, maximum permissible trickle charge current into full battery. Luckily it's an "industrial" battery so there is a datasheet.
Kevin.D:
I also found those rechargeable 9 V PP3's (7 or 8  1.2 V cells in series) really  problematic and they never used to last more than a few cycles before failing. I think the main cause of failure with them is over-discharge of one of the cells  (since they are not initially all equal or gradually become unbalanced over charging cycles) and then that discharged cell will  get reverse charged (which damages NIMH cells) by the  energized cells when used further. So the main thing with these is to never let them go empty before deciding to recharge , I now don't let mine get below about ~30% before they get a recharge .
 I decided the best charging strategy was to  trickle charge them @  no more than 15 mA for 12 hours+ as at this charge rate I don't think they can be damaged by overcharging and you can leave them on and be sure ALL cells are charged up to max capacity. I Use these cheap plug-in trickle chargers as they deliver about the correct charging rate (16-22 mA) max trickle charge rate before damage is about 25mA I have read . https://www.ebay.co.uk/itm/Uniross-Compact-Charger-for-AA-AAA-9V-PP3-2x-Lloytron-9V-Rechargeable-Batteries/111581125510?epid=1439684832&hash=item19fac0db86:g:KOMAAOSw5UZY-LbS .
 I really don't use a lot of rechargeable PP3's so can't really vouch for my method yet but have had only one failure out of 5
the other 4 are still going strong after about ~40 cycles.

Regards .
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