Checking an 18v Ni-CD Battery and charger.

bluenose1940 · April 14, 2022

I am trying to help a friend out with a problem with a strimmer.

The item has an 18v Ni-CD Battery and is charged with a Bosch AL60DV 2411 7.2 - 24v charger.

The problem is we don't know if the charger isn't charging or, if it is, the Battery isn't holding the charge.

There seems to be 4 connectors on the Battery, three of them are flat plates that are approximately 10mm square, there is one each side of the part that slots into the charger with one on the radiused part if it, the 4th one is a small pin that is on the + side. This pin doesn't seem to connect to anything in the charger and I don't have the actual strimmer with me at the moment so can't tell if there is a corresponding connector in the tool. If I put the multimeter on the two flat plates on the side, I am getting a reading of 19.51v which to my mind seems quite good. I also get this same reading if I put the probes on the + plate on the side and on the flat plate on the radiused part.

What sort of reading should I be getting from the actual charger? If I put the probes on the two connectors that come into contact with the side plates, all I am getting is a reading of 0.01v

I have attached a couple of images that may be of some help. Thank you for any help that may be offered.

NemesisUK · April 14, 2022

When was the last time the Battery was used/charged?

I had a second Battery to my drill and it deep discharged through lack of use and wouldn't recharge.

Herbie · April 14, 2022

I think the charger needs to be loaded in order to produce an output, which is why you're not getting a reading.

Try using a 12V car bulb across the charger terminals to see if it lights up.

I think 19.51V at the Battery is a bit low for an off-load reading but not too sure.

bluenose1940 · April 17, 2022

I charged the Battery again yesterday morning and the reading it gave was just over 19v, I noticed this morning that it seems to have settled at about 17.5v, is this too low for it to drive the strimmer effectively?

Can someone tell me if this will work please, I have an 18v Battery that belongs to my Makita drill, if I connect a couple of wires to the motor on the strimmer and then touch these wires on my 18v Battery, this should drive the motor and indicate if the motor is in good working order shouldn't it, or am I playing with fire trying that?

Herbie · April 17, 2022

1 hour ago, bluenose1940 said:

I charged the battery again yesterday morning and the reading it gave was just over 19v, I noticed this morning that it seems to have settled at about 17.5v, is this too low for it to drive the strimmer effectively?

According to the label it's an 18V Battery so 17.5V is probably OK. The problem is, what happens to the voltage when it's on load - it may be able to drive the strimmer alright but it may drop like a stone and be no good.

1 hour ago, bluenose1940 said:

I have an 18v battery that belongs to my Makita drill, if I connect a couple of wires to the motor on the strimmer and then touch these wires on my 18v battery, this should drive the motor and indicate if the motor is in good working order shouldn't it,

Yes, it should.

bluenose1940 · April 17, 2022

Thanks Herbie, is there any way that I can check the voltage when it's under load?

Herbie · April 17, 2022

10 minutes ago, bluenose1940 said:

Thanks Herbie, is there any way that I can check the voltage when it's under load?

Use the proper strimmer Battery in the same was as you're going to use your drill Battery, i.e. don't actually insert the Battery as you normally would, but just use two pieces of wire to connect the Battery to the strimmer and put your multimeter across the terminals of either the Battery or the motor. Or, if it's easier, cut each wire in half and rejoin them so that you have bare conductors halfway along each wire for your meter probes to clip onto.