guide me on a battery tester

[dragosios]

Any measuring instrument is as good as the user knowledge. It shows a value, but it's up to the humans to understand what this value mean.
As for measurements ... yes, a cheap multimeter is better than nothing. But the difference between a 3% plus some digits of a cheap multimeter and some very expensive ones with 6+ digits can be put to good use when measuring something important, designing things and so on. Such a multimeter is very expensive, it needs warm up time, even cheap cables can make a difference, so this is not something for daily use.
Overall, for somebody with enough knowledge, a cheap multimeter is enough if it works. But cheap multimeters are not so durable, during time they can have different problems even leading to errors, which again can be detected given enough knowledge.
A voltage tester, on the other hand, gives more reliability because is not so complex (when it comes to user interface) and probably even more durable since the error is not huge to be shown anyway. When you have 3-5 LED's as display, a 3% error is unlikely to show frequently..
P.S. A specific resistor in paralel with multimeters input is doing the same thing as a tester, just not as automated. Some analog multimeters have a lower impedance than modern digital ones and can be more accurate.

 

[chillinn]

when measuring something important

I think you're absolutely right, here, I just don't know what that might be where testing a cell as opposed to replacing a cell is more important. I can't say what they're using them for, but a friend of mine gets buckets of hardly used L91 from the surgeon his wife works for, because they replace them every time whatever device is used. I've worked in live reinforcement and before every show replaced the batteries in scores of lavaliere microphones even though nearly all of the cells had enough capacity for the entire three to six week run of the all the shows, but it was important enough not to have a microphone die that I did it, something like $100 in batteries wasted for every week the show ran. I guess the point I'm getting at is the question of when it is more important to accurately test a battery's capacity as opposed to replacing it with a fresh one, and I guess the answer is in those situations where there is no money being made and economy is important. So the focus becomes saving money; criticality is secondary.

 

[dragosios]

I completely agree. batteries are wasted sometimes.
Where I live we have a bin for recycling. If I take a quick look in that bin I find even new batteries or rechargables thrown out because they think are primaries, even 18650 which there is no way to look like a primary.
But in very simple words: a tester is enough to test. If you have some knowledge even that simple few dollars tester can be a very good tool for you. Sure, if you have the money to buy a more expensive one is even better.