Power tools generally come with 14.4v and 18v Li batteries , some even have 36v batteries. When a customer says 'my battery doesn't last' how do our technicians qualify this by testing and reporting accurately to the customer? I have a power tool workshop for 50 years but this is a new demand on our repair staff.

 

I am not entirely sure what exactly you need to test, but if you are interested in evaluating the overall battery capacity of a battery in Ah, you need a decent Electronic load (Maynuo, BK Precision, etc.) that will discharge and log its discharge curve. You need to compare this curve with what the corresponding discharge curve shown in the battery datasheet.

With this data in hand and taking into consideration other information (battery manufacturer's data, date of purchase, usage conditions, etc.) you have to make a decision if it either reached its end-of-life or is a defective unit.

 

Vehicle batteries can be tested by placing a very heavy load across the battery terminals and monitoring the volt drop. This technique is OK, because it is known that the battery must deliver well over 100A when cranking the engine.

The same technique cannot be applied across a range of power tool batteries, because the maximum current demand for each tool may differ significantly.

As rsjsouza says, you need to measure the battery pack capacity.

Below are links to a couple of instruments that may do what you want, measuring the Ah/Wh available from the battery pack.
On the down side, the test may take a few hours – normally a battery pack’s capacity is marked on its casing.
You might find that you have to make up leads as required to connect to the various packs customer’s want checked. Best to ask that the customers bring in the battery fully charged for testing.
At least you would then be confident of advising the customers correctly – you could even offer the service for a small fee, refunding if the customer purchases a replacement battery.

https://www.ebay.co.uk/itm/Battery-...676214?hash=item3afe4ebcf6:g:TcwAAOSwXB1bKb88

https://www.ebay.co.uk/itm/Multifun...m=292298095037&_trksid=p2060778.c100290.m3507

 

Vehicle batteries can be tested by placing a very heavy load across the battery terminals and monitoring the volt drop. This technique is OK, because it is known that the battery must deliver well over 100A when cranking the engine.

The same technique cannot be applied across a range of power tool batteries, because the maximum current demand for each tool may differ significantly.

As rsjsouza says, you need to measure the battery pack capacity.

Below are links to a couple of instruments that may do what you want, measuring the Ah/Wh available from the battery pack.
On the down side, the test may take a few hours – normally a battery pack’s capacity is marked on its casing.
You might find that you have to make up leads as required to connect to the various packs customer’s want checked. Best to ask that the customers bring in the battery fully charged for testing.
At least you would then be confident of advising the customers correctly – you could even offer the service for a small fee, refunding if the customer purchases a replacement battery.

https://www.ebay.co.uk/itm/Battery-...676214?hash=item3afe4ebcf6:g:TcwAAOSwXB1bKb88

https://www.ebay.co.uk/itm/Multifunctional-OLED-Current-Voltmeter-Thermometer-Battery-Capacity-Tester-10A/292298095037?_trkparms=aid=111001&algo=REC.SEED&ao=1&asc=20160727114228&meid=8eebc494446444d99ba5556e961f06a7&pid=100290&rk=2&rkt=4&sd=253374676214&itm=292298095037&_trksid=p2060778.c100290.m3507

 

Power tools generally come with 14.4v and 18v Li batteries , some even have 36v batteries. When a customer says 'my battery doesn't last' how do our technicians qualify this by testing and reporting accurately to the customer? I have a power tool workshop for 50 years but this is a new demand on our repair staff.

Hello there,

When someone says, "My battery does not last", there are a lot of interpretations of this statement and various connotations that the customer might be referring too. This means when you hear this you have to inquire a bit further into the issue they are having by asking more questions.

Some interpretations could be either one or a combination of:
1. The battery runs down too fast even after a full charge during my normal use.
2. The battery works ok when new, but after some time it starts to run down too fast even after a full charge.
3. The package construction could start to break down, such as the plastic cracking.

Number 1 and 2 would be the most common, with number 3 more rare unless they frequently drop the device so we could talk about those two.

Number 1 means that the cell is either of low quality or it has aged to the point where it does not hold a charge very well anymore. This is testable by doing an Ampere Hour Discharge Test.

Number 2 means that the cells quality may be high but it has aged and so the ampere hour test would show a good quality battery when new but that would drop off as time progressed while the battery was charged and used and charged and used again and again. The test for this would be to charge and discharge a battery many times while testing the ampere hours as above and see how fast the ampere hour capacity falls over time. Quality batteries will live up to their data sheet ratings, while low quality ones will of course die quickly.

Number 1 could mean the cell as aged, so you would have to inquire as to the number of charges and discharges the user has taken the pack through. You could estimate based on their daily usage habits.

 

Hi Hymie thanks for the answer, I handle automotive batteries for 50 years as well as power tools and have a carbon pile tester with volt and amp meter which is an infallible tester for the vehicle batteries , either the battery is good, weak ( reduced capacity) or dead! The same should apply to the Li tool batteries. I am an approved Bosch Power Tool Service Dealer since 1968 and the last few years NiCads have been discontinued in favour of the Li ones which are lighter, don't suffer self discharge so much and generally better performance. They seem to want to standardise all the tools to 3 voltages but at present Bosch has 108v , 12v , 14.4v , 18v and 36 volt. They have various capacity batteries 1.5 Ah ( which I think is being discontinued as too weak) ,
2.0Ah , 3.0Ah , 4.0 Ah . 5 Ah and 6 Ah. No doubt more will appear from other manufacturers like Makita and Metabo particularly. I have asked our Bosch technical man at Head Office here in Johannesburg for specs on all the batteries but as usual there is no information forthcoming from Bosch Power Tool Division , so we start on our own experiments. For example I made up 4 cables to run an 18v 115mm angle grinder with the battery remote connected by 200mm from the tool. With a DC clip on ammeter and a 4.0 Ah battery over the live cable I got 6 amps draw on idle and 36-37 amps on grinding with increased pressure until the grinder stalled. If you take the 37 amos times the 18v you get 666 watts which is in line with a 650 watt 220v similar grinder, so the logic is there. What I want to know is : what are the respective full load amp ratings of the
various battery sizes. I have 2 batteries with me , one is 14.4v 1.5 Ah and marked 21.6Wh , the other is 18v 1.5 Ah and marked 23.4 Wh , that may be watt hour? But what is the maximum amp draw you could get out of them, only to connect to a tool with remote wires and stall the tool with the amp meter on the wire. What do you think?

 

Hello there,

When someone says, "My battery does not last", there are a lot of interpretations of this statement and various connotations that the customer might be referring too. This means when you hear this you have to inquire a bit further into the issue they are having by asking more questions.

Some interpretations could be either one or a combination of:
1. The battery runs down too fast even after a full charge during my normal use.
2. The battery works ok when new, but after some time it starts to run down too fast even after a full charge.
3. The package construction could start to break down, such as the plastic cracking.

Number 1 and 2 would be the most common, with number 3 more rare unless they frequently drop the device so we could talk about those two.

Number 1 means that the cell is either of low quality or it has aged to the point where it does not hold a charge very well anymore. This is testable by doing an Ampere Hour Discharge Test.

Number 2 means that the cells quality may be high but it has aged and so the ampere hour test would show a good quality battery when new but that would drop off as time progressed while the battery was charged and used and charged and used again and again. The test for this would be to charge and discharge a battery many times while testing the ampere hours as above and see how fast the ampere hour capacity falls over time. Quality batteries will live up to their data sheet ratings, while low quality ones will of course die quickly.

Number 1 could mean the cell as aged, so you would have to inquire as to the number of charges and discharges the user has taken the pack through. You could estimate based on their daily usage habits.

Hi Mr Al, thanks for your reply and interest, I was busy replying to Hymie , so check out what I said and if you can add to that we will get to the bottom of testing Li tool batteries between us. My main interest is that my workshop staff can give a customer with a battery problem an accurate and technically correct answer , particularly as these little Li batteries are costing as much as a full size car battery , and the higher Ah ones are even more!

 

When a customer says 'my battery doesn't last' how do our technicians qualify this by testing and reporting accurately to the customer? .

Well why do you have to test at all ???? the customer is saying the battery doesn't holds much power ... it runs down too quickly .... Don't you believe him? ..He either has to buy a new battery or put up with the reduced capacity of the one he has.

All such products use 18650 cells , as do USB power banks which also have the same issue ... I've dismantled two USB power banks and both had cells with old spot welding marks , indicating they were used cells , probably salvaged from scrap laptop batteries ... this is a big industry in China , the cells which still have some life are salvaged and put in products hidden by a plastic case ...

If new cells were used in powertool batteries they should have at least 400 cycles before capacity reduced by 20% .... Manufacturers save a lot of money by using half dead salvaged cells or cheap cells not designed for high discharge rates in power tools. ....

One solution is to take out the old cells and replace with a recognised brand (sanyo , panasonic ) these are around $3 or $5 each ... then you know you have genuine good cells ... their life will be determined by the voltage to which they are charged to 4.2 V gives around 400 cycle (until a 20% drop)..3.93 V will give 4,000 cycles (but only 75% of 4.2V capacity).

High discharge rates do effect the life of cells , this maybe part of the problem .If a tool has a designed run time of less than 15 mins on a charge , this will stress the cells , and reduce life.

 

Well why do you have to test at all ???? the customer is saying the battery doesn't holds much power ... it runs down too quickly .... Don't you believe him? ..He either has to buy a new battery or put up with the reduced capacity of the one he has.

All such products use 18650 cells , as do USB power banks which also have the same issue ... I've dismantled two USB power banks and both had cells with old spot welding marks , indicating they were used cells , probably salvaged from scrap laptop batteries ... this is a big industry in China , the cells which still have some life are salvaged and put in products hidden by a plastic case ...

If new cells were used in powertool batteries they should have at least 400 cycles before capacity reduced by 20% .... Manufacturers save a lot of money by using half dead salvaged cells or cheap cells not designed for high discharge rates in power tools. ....

One solution is to take out the old cells and replace with a recognised brand (sanyo , panasonic ) these are around $3 or $5 each ... then you know you have genuine good cells ... their life will be determined by the voltage to which they are charged to 4.2 V gives around 400 cycle (until a 20% drop)..3.93 V will give 4,000 cycles (but only 75% of 4.2V capacity).

High discharge rates do effect the life of cells , this maybe part of the problem .If a tool has a designed run time of less than 15 mins on a charge , this will stress the cells , and reduce life.

 

Sometimes when a customer complains about the battery performance we ask him to bring the charger in to make sure, some leave the skinny 2 pin plug on the cable with a poor Chinese make adapter and it's often found proper contact isn't made and the charging isn't efficient. I still want benchmark figures for our Li batteries from Bosch, whether they will give or are capable of giving is another story.

 

Sometimes when a customer complains about the battery performance we ask him to bring the charger in to make sure, some leave the skinny 2 pin plug on the cable with a poor Chinese make adapter and it's often found proper contact isn't made and the charging isn't efficient. I still want benchmark figures for our Li batteries from Bosch, whether they will give or are capable of giving is another story.

Hi again,

I read your other post now.

You do know how to test for ampere hour capacity dont you?
You charge the battery to a full charge, then discharge while measuring current and voltage. When the battery voltage gets down to the min voltage for that battery (sometimes 2.5v sometimes higher) you end the test.
While the test is running you measure the current and integrate over time. That gives you the total AH rating.
For example, 10 amps for 15 minutes, 5 amps for 30 mins, would be 10*0.25+5*0.5=2.5+2.5 =5 AH.
That's with a resistive load. With a constant current, the current level is always the same so it's easier to calculate.

That's the main test for a battery that you want to check.

It's not hard to do by hand by measuring and checking every 10 minutes or so, but you can automate it with custom circuitry or just look for a tester that is already on the market. There are many for 18650 cells BTW if you can get to test each one individually. If not you'll need a more general purpose tester.

These kinds of tests provide you with actual numbers that you can compare. For example, if one battery tests to 5AH and another to 6AH, you know the second one is better.

It's nice to see that you understand a lot about these kinds of measurements and related.
.

 

Hi again,

I read your other post now.

You do know how to test for ampere hour capacity dont you?
You charge the battery to a full charge, then discharge while measuring current and voltage. When the battery voltage gets down to the min voltage for that battery (sometimes 2.5v sometimes higher) you end the test.
While the test is running you measure the current and integrate over time. That gives you the total AH rating.
For example, 10 amps for 15 minutes, 5 amps for 30 mins, would be 10*0.25+5*0.5=2.5+2.5 =5 AH.
That's with a resistive load. With a constant current, the current level is always the same so it's easier to calculate.

That's the main test for a battery that you want to check.

It's not hard to do by hand by measuring and checking every 10 minutes or so, but you can automate it with custom circuitry or just look for a tester that is already on the market. There are many for 18650 cells BTW if you can get to test each one individually. If not you'll need a more general purpose tester.

These kinds of tests provide you with actual numbers that you can compare. For example, if one battery tests to 5AH and another to 6AH, you know the second one is better.

It's nice to see that you understand a lot about these kinds of measurements and related.
.

 

Hi Mr Al, it's encouraging to get all this feedback and I am saving all the replies for studying, Bosch said today they do have a battery tester so I want to see one to ascertain if it is worth buying. As I said before I want my staff to give a customer a technically accurate answer when there is a battery complaint , for that we need the full specs of all voltage Li's and all Ah ratings, I will see if Bosch can come up with them , then we have a benchmark for testing. Thanks for your interest and information - I have some studying to do!

 

The problem with buying the Bosch battery tester is that it is only likely to be compatible with Bosch tools.

One thought on making electrical contact with other battery pack types (for the purpose of measuring the battery pack capacity) is to harvest the connection part/body of otherwise broken tools. Over time you would have a selection of tool parts allowing easy connection to the battery packs from differing manufacturers.

Although a heavy electrical load placed on the battery pack will give a good indication of battery health – the problem is the differing ratings of the packs. One pack might easily deliver 10A over a short period, whereas a low capacity pack might not despite the battery being new/good.
That is why others and I have suggested that the only way to go is to measuring the battery pack capacity in Ah or preferably Wh.

 

You do know how to test for ampere hour capacity dont you?
You charge the battery to a full charge, then discharge while measuring current and voltage. When the battery voltage gets down to the min voltage for that battery (sometimes 2.5v sometimes higher) you end the test.
While the test is running you measure the current and integrate over time. That gives you the total AH rating.
For example, 10 amps for 15 minutes, 5 amps for 30 mins, would be 10*0.25+5*0.5=2.5+2.5 =5 AH.
That's with a resistive load. With a constant current, the current level is always the same so it's easier to calculate.
That's the main test for a battery that you want to check.
It's not hard to do by hand by measuring and checking every 10 minutes or so, but you can automate it with custom circuitry or just look for a tester that is already on the market. There are many for 18650 cells BTW if you can get to test each one individually. If not you'll need a more general purpose tester.
These kinds of tests provide you with actual numbers that you can compare. For example, if one battery tests to 5AH and another to 6AH, you know the second one is better.
It's nice to see that you understand a lot about these kinds of measurements and related.
.

It's not quite that easy .... the available capacity is dependent on discharge rate ...... you can measure capacity at 1C and that will show what's available taking 1 Hr to discharge ... but powertools discharge much quicker and so 1C capacity will be much higher than what you get in practice due to internal resistance of cells taking a higher % of capacity at high discharge rates . Internal resistance increases with age .... the bosh tester is yet another trick to take more of your money ...

The obvious answer is to discharge by using the tool, see how long it runs ...But the owner has already done this and is telling you he's not happy!!!

Tell the owner bosh is using cheap cells that don't last in the high current demanded .... you can refurbish by putting in new cells of known specifications .... this should cost about half what bosh charges for a new battery ... you will have to get educated about cell specs , some are designed for higher discharge rates .

But the first thing to ask the customer is how often he uses the tool , how many times has he charged up the battery??? He should have hundreds of charges/discharges before a new battery is needed ,If the cells were good for the job

 

It's not quite that easy .... the available capacity is dependent on discharge rate ...... you can measure capacity at 1C and that will show what's available taking 1 Hr to discharge ... but powertools discharge much quicker and so 1C capacity will be much higher than what you get in practice due to internal resistance of cells taking a higher % of capacity at high discharge rates . Internal resistance increases with age .... the bosh tester is yet another trick to take more of your money ...

Actually, it is that easy because we choose a discharge rate that is reasonable and that usually means we have to duplicate the manufacturer's discharge rate when they test the battery, and that is usually C/20.
But whatever the choice is, the idea is to stick with that. That gives us a comparative figure that directly (well almost) translates to a decision about which battery is better than the other, and also how it stands in the test over time with other batteries of the same type. In other words, when they are all tested the same we come out with figures that we can use to judge the quality of the batteries.
I've been involved with these kinds of things for some 40 or more years now and i can tell you this is not a new concept. Manufacturers have done this for years, and buyers have used their information to choose battery types for their applications. It's true though that some manu's actually LIE about their ratings, but a quick test using a common industry test (like C/20) gives us a true result which we can use.
It's also true that any battery will test differently depending on load..it's colloquially referred to as the "P Factor". However, when the batteries are all tested using the same load current, we have a benchmark that we use to compare, and it obviously works.

The obvious answer is to discharge by using the tool, see how long it runs ...But the owner has already done this and is telling you he's not happy!!!

Sorry to say that might sound like a very sound idea because the tool after all is the real load. However, a tool used for various duties can draw a load current that can vary all over the place. My measurements of one tool took me from low current like 2 amps or something to 30 amps or more. You cant test a battery with a variable load unless you can vary it in exactly the same way for every single battery you test, and that obviously is not easy to do but most importantly not necessary. The standardized test outlined above is the test used for almost all batteries.
Of course there are other tests we can throw into the mix too, such as internal resistance, which is also a test sometimes used.

 

Hi Mr Al, it's encouraging to get all this feedback and I am saving all the replies for studying, Bosch said today they do have a battery tester so I want to see one to ascertain if it is worth buying. As I said before I want my staff to give a customer a technically accurate answer when there is a battery complaint , for that we need the full specs of all voltage Li's and all Ah ratings, I will see if Bosch can come up with them , then we have a benchmark for testing. Thanks for your interest and information - I have some studying to do!

Hi,

Real quick, dont they put that info right on the battery? That is, the AH rating.
Mine has this right on the battery itself: 3.0 AHr. Not a Bosch though.
Maybe this is a new concept though because my older drill did not have that info on it.

 

The problem with buying the Bosch battery tester is that it is only likely to be compatible with Bosch tools.

One thought on making electrical contact with other battery pack types (for the purpose of measuring the battery pack capacity) is to harvest the connection part/body of otherwise broken tools. Over time you would have a selection of tool parts allowing easy connection to the battery packs from differing manufacturers.

Although a heavy electrical load placed on the battery pack will give a good indication of battery health – the problem is the differing ratings of the packs. One pack might easily deliver 10A over a short period, whereas a low capacity pack might not despite the battery being new/good.
That is why others and I have suggested that the only way to go is to measuring the battery pack capacity in Ah or preferably Wh.

 

Hi Hymie, Thanks for that, we also get in non Bosch tools for repair so as you say the Bosch tester may only be good for Bosch. I did get a discarded Bosch 18v battery pack and took all the guts out of it , then I got a defective charger's casing and emptied that, I ran 4 wires from one to the other making sure the sequence was right. Now I have a rig that I can put a battery in and plug it in to the tool. The loose wires can then have a DC clip on ammeter connected. The weird thing is it works but the drill turns very slowly! I take battery out and put it direct in the drill and it runs fine! There is just straight wire to wire connection , no circuitry in between so I am puzzled. This happens with a 14.4v tool and an 18v tool. I milled off the ledge on the empty battery pack so it fits both voltages. Another mystery is that the batteries have 5 connections but the tools and chargers have 4. What is the unused connection for? Thanks again for your interest in this subject, I am getting more feedback from people on this site that I get from Bosch here in South Africa! How do you test the battery for Wh capacity?

 

Hi Hymie, I had the +- wire polarity wrong on my battery test rig and when I reversed it the drills ran fine. On an 18v drill with 1.5Ah battery we got 4 amps at idle and 12 amps at full load. Then I took a freshly charged 18v battery and we got 6 amps at idle and nearly 40 amps even still not stalling the drill! That would be 720 watts which is the wattage on a medium size 220v drill which is logical. It seems you can pull a much higher amperage out of the Li battery packs than people think, but we are not getting benchmark figures to use when a customer brings us a suspected faulty Li battery. The drill I used was one I ordered from stock from Bosch here but obviously they don't charge all the batteries fully before despatching them for sale , this one came with 3 x 1.5Ah batteries.