Rechargeable batteries

Crap charger.

Mike

Because the 9v batteries are a set of cells in series so the normal methods of detecting full charge do not apply (individual cells may be in a different state of charge). Hence the instruction to slow charge for a minimum interval that ensures that all cells are fully charged at a charge rate that is low enough not to damage through over-charge.

Chris K

Then how do power tool chargers manage it?

Mike

Extra "balance" connections between individual cells within battery and charger.

With multiple cell batteries you can't sense the change in terminal voltage in the same way as single cell types.

Much the same way I guess - and they still tend to use NICADs which are much more robust wrt charging. Lion power tools use more complex charging algorithms like laptops. Still not sure I like the idea of charging series connected Lions without individual cell monitoring but it seems to work for laptops and the like. Perhaps the cells are more carefully matched at the outset.

Chris K

Not for NiCads that I've seen. Just series charging of strings of cells. I have an EoR 36v (30 cell) battery pack I got from B&Q for £1 as a source of cells - just 30 cells in series.

Chris K

Maybe not NiCads but certainly for Lithium based ones, hence all the extra terminals on the pack.

Nicad power tool chargers use a different system based on temperature instead of terminal voltage changes.

Do you have a pointer to a 9v charger which will work differently then?

But power tools and laptops don?t get charged on time alone.

At a rough guess its because the single cell chargers can tel when its charged as there is only one cell, but as all 9v batteries have lots of cells in series, you will always find that you are overcharging some cells more than others making the detection of fully charged very ambiguous. If sad batteries had an internal circuit that could detect each cell then you could do this, but they don't. Brian

No see the answer I gave earlier. Brian