Battery 20v Lithium-ion not holding charge

Telegram Sam · Sep 24, 2021

1. I have an Aldi Cordless Hedge Trimmer, powered by a 20 V Lithium-Ion battery. It is manifestly under-powered - jams frequently - and their tec support cannot offer any advice ("At that price what do you expect?"!!)
I see however that you can run the machine with an optional 40 V battery. Question: Would this improve the power (torque) of the motor, or as I was told would it do no more than extend the interval between recharges?

2. I have a 12 v battery in the car which is "borderline" age-wise. I can charge it up to over 12 v but it is not very good at holding the charge. I have also a simple DIY multi-meter. When I test one with the other the reading fluctuates and I have to guess what the underlying value is. Is this likely to be an indication of the state of the battery, or of the multi-meter which is probably in the same age bracket? Can one get multi-meters with a "stabilised" read-out, and is it worth simple DIY people like me investing in one just for occasional use?

Advice on either (or both!) topics much appreciated.

SJD · Sep 24, 2021

Re (1), the 40V battery appears to be a dual voltage type, i.e. you can use it for 20V or 40V tools. With a 20V tool, you are just going to get a longer run time, it is not going to improve the motor power. Regard it as two 20V batteries in one case, with connections that allow them to be used in parallel (20v tool) or series (40V tool).

Re (2), personally if the battery is causing problems like the car not starting after sitting unused for days or a week or two, I'd just replace it - assuming you are sure it is the battery, and not something draining it e.g. some retrofitted audio gear etc. I'd regard the cost of a new battery pretty minimal when you think how much a tank of petrol costs, and not worth the inconvenience of not being able to just start and go.

Telegram Sam · Sep 24, 2021

Tks for your clear answer to Q 1. I will save myself the expense. But there are many 20 V battery op machines on sale. How can one tell the difference in power output between the bottom and top of the range?

Re 2 I have got a second battery for emergency use (ex scrapyard). I would like to feel a little more competent / have more trust in my use of the multi-meter though

Avo Mk8 · Sep 25, 2021

You don't mention whether your multimeter is an analogue (moving coil meter) display, or a digital one.
Either way, the reading should not be jumping about if the probes are clean and making good contact, and you are on the correct range for the job.
Assuming the multimeter measures ohms, and it has a good battery in it, does it give a steady reading (of about zero) when the probes are in good contact with each other? What if you measure the resistance of a filament light bulb? That should give a fairly steady reading. Have you tried measuring the voltage from a single AA or similar cell, which should give a steady value?

If the meter jumps about for all these, try some different bits of wire for probes.
If the meter still misbehaves, you need a new one ? !

However if the 12v battery gives unsteady readings, but the other tests I suggest are OK, you have a problem 12v battery, or charger, or both. If the battery reads steady off charge, but fluctuates on charge, you have a faulty charger or its connections.