Maker Pro
Maker Pro

Rechargeable Batteries Question

Maureen23669

Feb 14, 2016
3
Joined
Feb 14, 2016
Messages
3
I hope I have the right forum to ask this question. Just bought an Opus recharger, and tested all of my millions of rechargeable batteries. I know that I should be using batteries with the same level of charge when using more than one. But now I have voltage numbers, internal resistance numbers and mAH numbers. Which should I be matching?

Thanks!

Maureen
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
12,518
Joined
Nov 17, 2011
Messages
12,518
Hi Maureen,
welcome to electronicspoint.

Which should I be matching?
Ideally all.
Which combinations work depends on the application.
Typically batteries are operated in series. The voltages of the single cells add up to the voltage of the whole stack. Differences in single cell voltages are comparatively unimportant, as the voltage of the whole stack counts.
The same current flows through all cells (as in every series connection), so all cells are discharged in the same way. Therefore the capacity (mAh) of all cells should match as closely as possible. The cell with the least capacity will be discharged first and has a risk of being reversely charged, the polarity may swap and the cell can be destroyed.
The series resistances of the single cells simply add up to the series resistance of the whole stack. The effect is voltage drop across the series resistance under load and heating of the cells due to power dissipation in the series resistance. There is no need to match the series resistances of the cells.

Make sure you charge the cells as single cells, not as a complete stack. This will optimize the lifetime of the batteries.

Here is useful stuff to read about batteries.
 

Maureen23669

Feb 14, 2016
3
Joined
Feb 14, 2016
Messages
3
Hi Maureen,
welcome to electronicspoint.


Ideally all.
Which combinations work depends on the application.
Typically batteries are operated in series. The voltages of the single cells add up to the voltage of the whole stack. Differences in single cell voltages are comparatively unimportant, as the voltage of the whole stack counts.
The same current flows through all cells (as in every series connection), so all cells are discharged in the same way. Therefore the capacity (mAh) of all cells should match as closely as possible. The cell with the least capacity will be discharged first and has a risk of being reversely charged, the polarity may swap and the cell can be destroyed.
The series resistances of the single cells simply add up to the series resistance of the whole stack. The effect is voltage drop across the series resistance under load and heating of the cells due to power dissipation in the series resistance. There is no need to match the series resistances of the cells.

Make sure you charge the cells as single cells, not as a complete stack. This will optimize the lifetime of the batteries.

Here is useful stuff to read about batteries.
Thanks, Harald!
 

Martaine2005

May 12, 2015
4,218
Joined
May 12, 2015
Messages
4,218
Make sure you charge the cells as single cells, not as a complete stack. This will optimize the lifetime of the batteries.
Hi my mothers name sake (Maureen),
Harold has a good reason for mentioning that paragraph.
Think "tool batteries", they normally always fail because of one faulty cell. IE, lots in series, rather than charged individually.
If you do indeed have "millions", I am also sure that lots are old nicad style cells. You can charge and discharge these several times to try and remove "memory effect" which plagued these batteries and left most useless.
Knowing how to treat a rechargeable battery is important too. It can last many charges longer than the manufacturer specifies.
One good way is to always drain (discharge) the battery before putting into storage or not using for a long time.
But all other questions have been answered by Harold. (good 'ole' Harold).

Martin
 

Maureen23669

Feb 14, 2016
3
Joined
Feb 14, 2016
Messages
3
Hi my mothers name sake (Maureen),
Harold has a good reason for mentioning that paragraph.
Think "tool batteries", they normally always fail because of one faulty cell. IE, lots in series, rather than charged individually.
If you do indeed have "millions", I am also sure that lots are old nicad style cells. You can charge and discharge these several times to try and remove "memory effect" which plagued these batteries and left most useless.
Knowing how to treat a rechargeable battery is important too. It can last many charges longer than the manufacturer specifies.
One good way is to always drain (discharge) the battery before putting into storage or not using for a long time.
But all other questions have been answered by Harold. (good 'ole' Harold).

Martin
Thanks, Martin. They're all NiMH. But I always leave them charged so the're ready to go, even though I don't go much anymore, with an empty nest.

Not Mom (unless you've changed your name for security)
 

Martaine2005

May 12, 2015
4,218
Joined
May 12, 2015
Messages
4,218
Thanks, Martin. They're all NiMH. But I always leave them charged so the're ready to go, even though I don't go much anymore, with an empty nest.

Not Mom (unless you've changed your name for security)
Noooo, my mothers name is Maureen too....
I still think the same rule applies. Store rechargeables discharged.. Unless it's a week or two before using them.
Even then, after two or three days I would fully charge them before going out. (assuming you are talking RC flying).
If they are old and you don't trust them for flying, better to replace them.

Martin
 
Top