Internal Resistance and Voltage drop among NIMH recharageable batteries.

I'm wondering if these values are meant to be consistent among all NIMH rechargeable batteries. Or if, for example, it's normal for eneloop pro's or maha imedions to have different values than standard eneloops due to their higher capacity.

I ask because I've noticed a trend among my eneloops, they all seem to have 1.5v internal resistance and a voltage of around 1.15-1.2v under load. My maha imedions however are giving me 1.6-1.7v of IR and a voltage of about 1.09v under load. So I'm unsure if these cells are spent or if this is normal for high capacity NIMH.

llmercll said:

I'm wondering if these values are meant to be consistent among all NIMH rechargeable batteries. Or if, for example, it's normal for eneloop pro's or maha imedions to have different values than standard eneloops due to their higher capacity.

I ask because I've noticed a trend among my eneloops, they all seem to have 1.5v internal resistance and a voltage of around 1.15-1.2v under load. My maha imedions however are giving me 1.6-1.7v of IR and a voltage of about 1.09v under load. So I'm unsure if these cells are spent or if this is normal for high capacity NIMH.

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Higher capacity NiMH cells will suffer more quickly from cycling. So, it's normal that you're seeing your high capacity cells wear out more quickly than standard Eneloops.

1.09v under load doesn't sound too bad, depending on what load you're using. You can use this site to check the voltage under load for new cells, from a whole range of AA cell types:

https://lygte-info.dk/review/batteries2012/CommonAAcomparator.php

I wouldn't discard the cells until they get below 1.0v under a load of a couple of amps, using a freshly charged cell.

Hello Llmercll,

As you have noticed, higher IR = lower voltage under load.

When the voltage under load becomes unacceptable, the cell needs to be recycled.

In general, higher capacity cells have higher IR.

Tom

So even new high capacity NIMHs have higher IR? Or is it mainly because they have shorter lifetimes?

llmercll said:

So even new high capacity NIMHs have higher IR? Or is it mainly because they have shorter lifetimes?

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Mostly yes, and yes. Generally, high capacity cells have higher internal resistance. I'm not sure that's necessarily true when you compare standard Eneloops with Eneloop Pros, as they're pretty close. Eneloops have the lowest resistance for NiMH batteries. Other brands tend to compete more on capacity, and will have significantly higher internal resistance.

Those high capacity cells will wear out very quick, too. That drops their capacity, and sky-rockets their internal resistance.

I stay away from high capacity cells. Standard Eneloops are fine for most of my applications, and they last for many years. When I need more capacity, I use lithium-ion.