Topping off Charging & initial self-discharge

[Phlack]

Still trying to grasp the initial self-discharge topic.

Suppose I take a typical NiMH battery, let's say 2500mah. Doesn't matter if it's hybrid or not, since, from what I understand, the initial self-discharge happens in both kinds; it's just the discharge afterwards is different.

Let's assume the initial self-discharge is 20% for the first 24 hours.

A fully topped off charge of the battery would, theoretically, "fill it" to 2500mah. 20% of that is 500mah, so after 24 hours of sitting off the charger, the battery would be 2000mah.

What if I only charge it up to, say, 2250mah, or ~90% of the capacity (that's what the Maha C808M seems to do anyway)...will there still be a 20% discharge (bringing it down to 1800mah), or would it bring it to 20% below the max, which would then be the 2000mah?

What if I only give it a half charge...ie to 1250mah? Would there be an initial self-discharge at all?

Basically at what point does the initial self-discharge take place and how long does it last?

Thanks
-Mike

 

[SilverFox]

Hello Mike,

The 20% figure is optimistic.

The cells rated capacity (if the cell is from a manufacturer and not simply a re-labeled brand) is based on waiting at least 1 hour after charging before doing the discharge test. The highest rate of self discharge is when the cell is "hot" right off the charger. When the cell cools off, the self discharge rate drops to a much lower rate.

The highest self discharge rate occurs at the highest voltage. As the voltage drops, so does the self discharge rate.

The first post of this thread has some self discharge rate curves in it. They may help you get a better understanding of how self discharge works.

Tom