warning recharging classic ni-cd battery packs

[Don Shepherd]

I have always recharged my HP-65 rechargeable battery packs overnight when the LED's start to flicker. The battery pack was due to expire after 3 years, which would be next month. I thought I would check on the recharge after a couple of hours and I am glad I did. The back of the 65 was very hot, and part of the battery cover had melted. I removed the pack and it was hot.

Fortunately, the calc still appears to be working fine.

I'm not going to use rechargeable cells anymore, just regular AAA's in a small case designed to hold them.

So beware of recharging ni-cd batteries if they are about to expire.

[EugeneNine]

NiCad's expire?

[Don Shepherd]

(12-10-2019 01:27 AM)EugeneNine Wrote:  NiCad's expire?

The batt pack says "remove the battery after 3 years to prevent corrosion damage" and there is a place you can write in the removal date. I wrote in "January 2020" when I got the pack 3 years ago, in 2017.

[EugeneNine]

Thats really odd. Used to be NiCad's were the longest life unless they got cooked by a simple 'dumb' charger. I used to get a decade out of them.

[mfleming]

This is why I use Eneloops in a rebuilt battery pack. Get them from a familiar source on TAS or make one yourself, then recharge those batteries *externally*

Glad your calc is OK, but you may want to add your name to the .stl file request

[Don Shepherd]

(12-10-2019 01:48 AM)mfleming Wrote:  recharge those batteries *externally*

I see the wisdom of that now! I'll have to consider that.

[eried]

(12-10-2019 02:14 AM)Don Shepherd Wrote:  

(12-10-2019 01:48 AM)mfleming Wrote:  recharge those batteries *externally*

I see the wisdom of that now! I'll have to consider that.

I always charge all my batteries with https://www.skyrc.com/iMAX_B6mini_Charger
It supports all battery types and you can attach a velcro strap with a temperature sensor.

It would be interesting if you could measure the internal resistance of those damaged NiCD (with a charger, or multitester). At least in LiPOs, that value reflects the "health"of the battery.

[Don Shepherd]

(12-10-2019 09:47 AM)eried Wrote:  

(12-10-2019 02:14 AM)Don Shepherd Wrote:  I see the wisdom of that now! I'll have to consider that.

I always charge all my batteries with https://www.skyrc.com/iMAX_B6mini_Charger
It supports all battery types and you can attach a velcro strap with a temperature sensor.

It would be interesting if you could measure the internal resistance of those damaged NiCD (with a charger, or multitester). At least in LiPOs, that value reflects the "health"of the battery.

thanks eried, that looks like a good charger, I'll keep it in mind if I decide to return to rechargeables.

I threw that damaged pack away, I was so mad at it. The battery cover on my 65 is a bit warped as a result of the overheating, but the calc itself is fine, fortunately. One plastic slide on the cover works fine but the other does not, but one slide is enough to hold it in place.