I have one of those cordless screwdriver http://www.canadiantire.ca/AST/brow...craft+3.6V+Pivoting+Screwdriver.jsp?locale=en and the battery pack (4 1.2V NIMH) batteries discharge as soon as I push on the trigger it goes from 4.8V to 0 in no time. Would it be safe to replace the 4 pack NIMH with a 4 pack lithium ion batteries?

 

I have one of those cordless screwdriver http://www.canadiantire.ca/AST/brow...craft+3.6V+Pivoting+Screwdriver.jsp?locale=en and the battery pack (4 1.2V NIMH) batteries discharge as soon as I push on the trigger it goes from 4.8V to 0 in no time. Would it be safe to replace the 4 pack NIMH with a 4 pack lithium ion batteries?

yes.. but try considering testing the batteries out more if they are the parts that malfunction..

 

Li-Ion batteries are 4.2V/cell and Ni-MH are 1.4V/cell..... they are not interchangeable no way, no how.

 

Are you saying that no matter the size of the batter a Li-Ion battery has cells with 4.2V max and for NIMH 1.4V? Just trying to understand more about batteries

 

Are you saying that no matter the size of the batter a Li-Ion battery has cells with 4.2V max and for NIMH 1.4V? Just trying to understand more about batteries

Correct. A single Li-Ion cell is 4.2V full charge, drops to about 2.9V end of cycle.

A Ni-Mh or Ni-Cd cell is 1.4V full charge and about 1.1V end of cycle.

Your 4 cell Ni-Mh battery is 5.6V full charge and about 4.5V end of discharge cycle, so it is basically a 5V battery.

There is no way to get a single or dual cell Li battery with a compatible voltage.

 

Well if it's a screwdriver then you could probably get away with wiring one or two Li-Ion cells in parallel. It wouldnt be as fast ,especially towards the end of the cycle but it's a screwdriver so that wouldn't be much of a problem .
Nevertheless check your circuitry first , batteries don't usually act that way .
How do you know that the batteries drop from 4,8 to 0 volts?(where did you put your probe)

 

Why don't you just open it up and replace the cells with NiMH? The cells may not be standard sizes but you can probably find an exact match on ebay, brand new cells. Just requires some solder tabs and a bit of soldering to make a brand new pack for yourself.

 

I opened it Replacement batteries are about $15-$20 on ebay with shipping I bought the Li-Ion version today on sale for $25. I tought it wasn't safe to solder wires or tabs to any kind of battery? The ones on ebay comes with the leads.

 

Correct. A single Li-Ion cell is 4.2V full charge, drops to about 2.9V end of cycle.

A Ni-Mh or Ni-Cd cell is 1.4V full charge and about 1.1V end of cycle.

Your 4 cell Ni-Mh battery is 5.6V full charge and about 4.5V end of discharge cycle, so it is basically a 5V battery.

There is no way to get a single or dual cell Li battery with a compatible voltage.

So the reason why it's not compatible is that the voltage issue or it's a charger issue? Meaning a circuit to charge a Li-Ion battery is different and not compatible to charge NIMH batteries?

 

So the reason why it's not compatible is that the voltage issue or it's a charger issue?

both

Meaning a circuit to charge a Li-Ion battery is different and not compatible to charge NIMH batteries?

correct. Improperly charging Li-Ion can cause fire.

 

both

correct. Improperly charging Li-Ion can cause fire.

Also if i'm not mistaken Li-Ion needs protection circuitry so the battery doesnt discharge below a minimum voltage after which it would stop working or work badly .