WANTED: reliable 9v NiMH battery!

[13hm13]

While I can't say I've tried every brand/model, I've tried quite a few and ...long story short ... they just don't last. One of the most disappointing cases is stuff from Powerex (Maha Energy), a Japanese company that's been around a while. A few years ago, I purchased several true 9v (claimed 9.6v) ... 6 mos. later, they all rapidly began to crap out. I thought I got a bad batch, but they were out of warranty so SOL! In 2010, I tried Maha's Imedion 9.6 v (230mAH) -- got two (they are $16 each + S/H). They lasted maybe 7mos.

My use: in a headphone amplifier, maybe 1hr use every other day (= very gentle use). Never abused (e.g., dropped, exposed to temp. extremes, used non-Maha charger, etc.)

How were they charged? ... via Maha's equally troublesome $40.00 charger.

Purchase Warning: Maha's other batts. (AA, AAA) and chargers are equally troublesome**, but at least one has decent alternative, like Sanyo eneloop.

Bottom line: a putative high-tech and well-established Japanese company. And their stuff ain't cheap. Reminds me of some luxury British or French cars ... not cheap, brand appeal ... but WRT long-term reliability ... forget it!

** About MAHA's chargers. I own three (MH-C204W, MH-C9000, MH-C490F 9V). Extremely sensitive .. even to their own-brand MAHA batteries. If the battery (internal resistance??) is a pubic hair off, you get the red blinking fault LED

[IanB]

Several points raised here, but let's focus on the 9 V batteries.

The first thing to be said is that 9 V NiMH batteries are inherently a bad idea. There are limits to what you can expect from them. If you want a better rechargeable solution you should consider Li-ion batteries instead. Something like the ones on this page:

http://www.batteryjunction.com/9v-lithium.html

So, 9 V NiMH--what's the problem with them?

The basic problem is that such batteries are made from 7 or 8 cells in series. Anyone who has worked with NiMH technology will recognize such a configuration as a "battery pack", and will know that managing an 8 cell battery pack needs particular care. You must keep the cells balanced during charging, and you must not over-discharge the pack.

A 2 hr charger like the Maha C490F is not good for long term use. A 2 hr charger has minimal balancing capability. For balancing you need to do a slow timed charge overnight for 12 to 16 hours at a low charging current. Ironically some of the cheaper "overnight" chargers you will find in retail stores are just about perfect for this.

The second problem with 8 cell packs is over-discharging. If you run the pack until the voltage fades, then it is almost certain that one of the cells inside the pack has become completely empty and has been subjected to voltage reversal. Over discharge to the point of voltage reversal is a sure fire way to kill an NiMH cell. And once one cell inside the battery has gone bad the whole battery will need replacing.

So, tip one for looking after such batteries is to recharge them long before you think they are empty. If you think the battery can run for three days before fading, then recharge it after two days while it is still going strong. Avoid running the battery down to fading power at all costs.

Tip two is to avoid fancy expensive chargers. Get an overnight trickle charger and charge the battery for a calculated amount of time. If the battery is 250 mAh, then charge it with a current not more than 25 mA and time it to 120%. E.g. 250/25 + 20% = 12 hours.

You can use a fast two hour charger two or three times in between slow charges if you are in a hurry, but always do the slow overnight charge at regular intervals.

[13hm13]

Yeah ... know about most of the points you made. I considered the Li-Po 9v, but the $$ and then the special charger! 9v is a popular size but I don't see a whole lot of NiMH models ... even Sanyo seems to stay clear.
Maybe there is just not enough demand for rechargeable 9v for the supply side to justify R&D investment ... that 9v li-Po has been around for over 10 years, I believe w/o much change in design and unit price.

A few yrs back, I did take a peek under the hood of the non-Imedion, older 9.6v Powerex ...
(if the charging issue wasn't enough, the (-) connector snapped off, so I had to rig)...

You can see ALL the indiv. cells!

[Psi]

Try Varta brand, they are usually pretty good.

Failing that it might be worth trying to fit one of those 1.5V -> 9V converters inside.

[nukie]

Maha Energy is a Taiwanese company founded in 1993. Some of their Powerex cells are made in Japan, probably Twicell factories. Get your facts right before you write.

While I can't say I've tried every brand/model, I've tried quite a few and ...long story short ... they just don't last. One of the most disappointing cases is stuff from Powerex (Maha Energy), a Japanese company that's been around a while.

[13hm13]

Get your facts right before you write.

Forums exist to clarify one another's "facts", not post one-more-comment for post-count bean counters. I suggest Dave ban you from this forum ... or at least suspend you until you know how to respond more ... uh ... politically   O0

[Rick Law]

While I can't say I've tried every brand/model, I've tried quite a few and ...long story short ... they just don't last. One of the most disappointing cases is stuff from Powerex (Maha Energy), a Japanese company that's been around a while. A few years ago, I purchased several true 9v (claimed 9.6v) ... 6 mos. later, they all rapidly began to crap out. I thought I got a bad batch, but they were out of warranty so SOL! In 2010, I tried Maha's Imedion 9.6 v (230mAH) -- got two (they are $16 each + S/H). They lasted maybe 7mos.
 ....

Have you tried TEnergy Centura?  I wrote this mini-review 9 months ago.
https://www.eevblog.com/forum/reviews/tenergy-centura-9v-and-tn141-mini-review/

I got a pair then.  One has been in my UT61E at near constant use and often forgot to turn off.  Sometimes, when I am doing long duration logging, I just wire it to a wall-wart while the battery is still in the UT61E.  (ie-wallwart charge it back up then hold the battery at about 9.3V while the UT61E is ticking and logging whatever it was measuring.)

After such punishment for 9 months, the other night, it ran day and a half straight and I plug the wall-wart back in (to make sure I can finish logging since I didn't know if it was fresh when I started the logging the morning before).

I found it very robust so far.
https://www.eevblog.com/forum/reviews/tenergy-centura-9v-and-tn141-mini-review/

[13hm13]

Thx for the review link.

I am familiar with that brand, but have never tried them.

I have tried a cheap Chinese 8.4v brand, that lasted about as long as 4x $ Maha.

The best "9v" of the several I've run into is Energizer (Made in Germany) ... it's about 6 years old, but not  useful in my apps because it is ONLY 7.2V (150mAh) ... its "durability" may not be all that surprising because of fewer comprising cells.

As a side note, the 9v batt. for the headphone amp noted earlier was just for convenience. That amp actually performs better with higher voltage (up to 24v). So my poor luck was serendipitous -- it  forced me to construct a 14v batt. pack, comprised of six AA eneloops -- I lose a little in convenience (remove all six to charge, rather than just one 9v ) but I gain quite a lot in total run-time and, most important, big gain in audio fidelity.

Back to 9v batts ...
For 9v use, for the same amp, I built a battery charge indicator: A comparator and a little bit of external circuitry can drive a bicolor power LED that changes color based on the battery voltage: green for a fresh battery, amber for one nearly used up, and red for “charge me now!”. The RED condition also fades as the batt(s) further discharge. And it's an ON/OFF idiot light, too. A "single" LED can convey so much info!

[IanB]

it  forced me to construct a 14v batt. pack, comprised of six AA eneloops

6 x 1.2 V = 7.4 V? 

[peter.mitchell]

it  forced me to construct a 14v batt. pack, comprised of six AA eneloops

6 x 1.2 V = 7.4 V? 

I feel it may be a +/- 7.4, = 14.8 with center tap, because he said it was for an audio amplifier. Who knows though.

[TheBay]

I swear by GP Branded NiMH 9v cells.

[saturation]

I've not had problems with GP or Maha 9V [ over 7 years old each], and I have 12 Centura tenergy 9V.

When they start to 'die' you need to cycle them, just as the Maha C9000 has a 'refresh' or cycle mode for 1.25V cells.

Its one reason to own a eload, like the Array 3371a.  You can cycle any cells without overdischarging them and restore NiMH to like new.  You can also calculate their new AH. 
 

[profmason]

Another thumbs up for the tenergy centura 9v. We replaced all the multimeter batteries in  3 student labs with these.  Of the 60 batteries we have had 0 failures in eighteen months. Batteries are trickle charged every 4 months or as needed.
We buy them from all battery in the US. 

[madires]

I'm using a few ANSMANN maxe (ready-to-use type) for the last 2-3 years without any problems.