I Proved Ni-Mh batteries do have a memory

Geo-TH,In

Well-known Member
It's cold outside and I need something to do. So, I decided to load test my 18v Ni-Mh batteries with a cordless saw and a block of wood. I would see how may inches each battery could cut at a depth of 2.25 inches. All batteries tested came off charger. I wrote on battery with a sharpie the number of inches. Then I used drill, work light and finally shop radio to drain battery to 16.5 volts. The shop radio shuts off at 16.5v which is 1.1v per cell.

Used Dewalt DC9310 charger, an old B&D slow charger and shop radio to charge batteries. Then kept all batteries warm in my battery warmer.

My findings prove that by draining batteries to 16.5v, letting them cool off before charging, does erase their memory and the amount of sawdust they make more than doubles. My worst battery yesterday would only cut 10 inches. Today it went 73 inches. I stopped cutting at 73 inches and measured the volts. All my batteries that made 73 inches had 18v or more.

IMHO this proves that Ni-Mh batteries really do have a memory. I'm sure someone may disagree with my findings.
geo
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I am a little more than confused ? So when you first cut the wood the saw quit and then you farther drained them down with the other tools ?
If so that makes me see it a little better. And if so you were before charging them before being FULLY drained and then they would not perform as well.
 
MikeM,

Sorry for the confusion.
Day one: Took batteries off charger, they were fully charged.
I used red oak, cut 2.25 depth. Measured distance of cut. I stopped when saw blade stopped. Then I finished discharging using a drill, light, and finally the radio. At that point battery voltage was 16-16.5v, 1-1.1v per cell. Let battery cool off before charging.

Day two. Used saw to make more sawdust. The worst battery on day only cut 10 inches. Today, I stopped it at 73 inches and it was measuring 18.8 volts. All batteries cut way more wood today. 3 other batteries made it to 73 inches and their voltages were above 18v.

Two batteries showed improvement, but didn't make it to 73. I'm draining all batteries a second time before charging. I charge batteries in my battery warmer and wait for them to cool off after fully discharging.

Hope this clears up the confusion. Bottom line, Ni-Mh batteries do have a memory like their cousin Ni-Cds.
geo
 
That's likely a good part of the reason I don't get along well with battery operated things. Other part is I don't use them much at all. Then when needed they are either dead or don't last very long and then dead.
Been liking the Honda EU1000 inverter generator I picked up on craigslist for a really good price. Makes corded tools more portable.
 
MikeM,
I have corded tools and two 3500 watt RV generators for portable power.

I'm down to 8 rentals and have to make repairs away shop. My truck is another workshop and a tool box on wheels .

I love my cordless tools come in handy. Won't be without.
George
 
Loren,
Having cordless tools is only a convience. I have same corded tools.

I was proving something Guido posted, Ni-Mh batteries, like Ni-Cds. both have a memory and by totally draining them you can wipe out the memory.

It's also a know fact that batteires doesn't like extreme heat or cold. So I built the battery warmer so I can keep batteries in cold pole barn.

Like you, I like to make things. In the winter I get bored and I have time to get inventive.

BTW, how is your dump trailer coming? When it comes to welding, I'm a self taught novice. I would never attempt to do the neat things weld together. I wish I had something to weld, but I have to weld outside because my shop would fill with smoke from burning rods. Too cold for me to even think of welding.
geo.
 
Back when I was building comercial steel frame buildings, We had to put the 18V dewalt chargers into the refrigerator of my site trailer during the summer to charge the 4 bats we were using in two drill drivers. They wouldn't charge when they were hot. We switched to Makita NiCad powered impacts and never looked back. The impacts were much lighter, charged during heavy use, and also relieved my wrist problems from the counter twist when the self tapping screws seated. We drove in thousands of TEK screws with them, even into I beams with the fine threaded self tappers.
Loren
 
Loren, Well 20 years ago I tried Makitas with the long battery case that went in the handle. Then switched over to Ryobi. Back then, neither would last very long. Batteries and tools both broke. Then I switched over to Dewalts and never had a tool issue, but their batteries suck. That's why I switched over to aftermarket NiMh batteries. IMHO, they last longer than NiCds and I hate Li ions.

So I guess we all like different things and have had different experiences.

It really doesn't really matter if you like blonds or red heads. All Ni batteries have memories and don't like the extreme temperatures.
Geo
 
Highly recommend a thorough reading of the battery university site, with its many and updated pages. On its page of discussion of nickel-based batteries, regarding NiMH cells, in 'advantages' it says "less prone to memory than NiCd.". It doesn't say 'no memory effects'.

Lots of good info about all battery types on the site. I always learn something new every time I go to it.
Battery University site by Cadex
 
Yes, I've read the articles form battery university. Also read batteries are like people, they don't like it too hot or too cold. They must have proper chargers because they don't like to be under or over charged.

They don't take kindly to someone removing hot battery from tool and expecting to recharge it right away. I carry enough batteries I put my dead batteries on the truck seat to cool off. Charge them hours later. In winter I put batteries on bed floor and blow warm air on them. Drop them in truck charger to top the charge off before I use them.

I was surprised just how much of a difference erasing the memory of my Ni-Mh really made.

Cutting oak with circular is a real good way to load test batteries too.
 
Well sir he did say that he had nothing to do (due to the weather) so looks to me like he took the initiative to amuse himself with something educational. My hat's in his ring!
 

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