Battery voltage vs capacity

Thread Starter

danielmutong

Joined Oct 26, 2019
8
Hi,

What is the relation between the voltage of a battery and it’s capacity(Ah)? Like when a battery is charged to its charge voltage, does that mean that the max capacity (Ah) has been reached?
Thanks
 

dl324

Joined Mar 30, 2015
16,846
It's not that simple.

Voltage is more a function of battery chemistry. Some batteries have a relatively stable output voltage until they're near exhaustion, some don't.

AH capacity can't be accurately predicted by open circuit voltage. I have a pile of batteries that have little capacity right after being charged. I set them aside (mark them) so they don't get used with stronger batteries. Stronger batteries in series with weak ones can abuse them, by forcing them in to reverse voltage, further accelerating their demise. That's why manufacturers of batteries and things that use batteries warn you to not mix old and fresh batteries or to mix battery chemistry.
 

Audioguru again

Joined Oct 21, 2019
6,674
go to www.batteryuniversity.com and read about charging the different types of batteries.
A Ni-MH battery has a voltage hump when it is fully charged.
An older Lithium battery voltage rises as it charges then when it reaches its maximum voltage of 4.20V per cell it is about 70% fully charged and it keeps charging with current but the voltage is supposed to stay at 4.20V. When its charging current drops to a low amount then it is fully charged.

Voltage vs capacity:
1) A little AAA Ni-MH battery is 1.4V and 850mAh when fully charged.
2) A larger AA Ni-MH battery is 1.4V and 2300mAh when fully charged.
3) The little Lithium batteries for my RC model airplanes are 8.4V and 150mAh when fully charged.
4) The larger Lithium batteries for my RC model airplanes are 8.4V and 450mAh when fully charged.
5) The little lead-acid battery for a motorcycle is 13.8V and 12Ah when fully charged.
6) The larger lead-acid battery for a car is 13.8V and 65Ah when fully charged.
 

ci139

Joined Jul 11, 2016
1,898
the terminal voltage of the charging and also the actual capacity depend on many factors , such as :

the aging of the battery (is depending on it's usage history),
the battery temperature ,
the charging rate ,
less the charging profile

but for the healthy batteries of the same type ( , the "same" ageing , temperature) the inter battery voltage difference is around 1% ** at the end of charge - which does not hint much about their possibly larger capacity differences /!\ . . .

** -- the Voltage is set by the chemistry Galvanic_cell , Cell_voltage - Wikipedia and for the similar relative placement of the electrodes and for the similar concentrations of the chemicals around the cell -- the voltage is basically a constant.
 
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