Update  ,I got the test meter from Harbor freight today ,i so i tested the  rechargeable batteries that my computer said needed to be changed & on the meter it shows that a 1.5 v should be 4.0ma ,when i tested it ,it read 3.5 ma ,so  does this battery need to be recharged ?, i also tested a new rechargeable never used yet & it came up as 3.5ma ,so is the battery that i took out of my keyboard really low on power ? i don't understand what if anything did i do wrong ,both the new rechargeable & the one that was supposedly low show the same reading ,i don't understand what is going on . Any help is appreciated .

I would say use the battery until the keyboard does not work then charge it.

You can not get a good amp reading without a load on the battery and most amp meters are installed in series with the battery

Charlie

Charlie ,i was aware that there needs to be a load on the battery to get an accurate reading ,when i saw that this tester had an option on the meter to test these batteries i thought that it had a load built into the meter ,thats why i bought it ,but i like your idea just use the batteries until my keeboard doesn't work sounds like the best way to go .

... i thought that it had a load built into the meter

It's a 370 Ohm Resistor load; the HF "manual" calls it a 370 mW load.  Whatever.

The math is Ohm's Law:   Current = Voltage / Resistance.

1.5V battery.  Current = 1.5 V / 370 Ohms = 0.004 Amps = 4 mA

9V battery.  Current = 9V / 370 Ohms = 0.024 Amps = 24 mA (close enough to 25 mA)

When you read "only" 3.5 mA with your rechargeable it's because the battery voltage was about 1.3V under the 370 Ohm load.  Current = 1.3V / 370 Ohms = 0.0035 Amps = 3.5 mA

As to whether 1.3V is "low" is a function of how your electronics gadget was designed.  There is a so-called voltage-discharge-curve which characterizes how the voltage in a battery drops over time.  Problem is it depends on many things from the battery chemistry, the temperature, the load current, etc..  At some point in the design of your electronic gadget, an engineer had to choose a voltage threshold below which the "low battery" icon turns on.  And because of the variations in the discharge curve between battery types, a "low battery" can mean vastly different actual remaining operating time.

Last edited by stan2004

Gerald, Stan's calcs are correct.  Note that if you use NiMH batteries, you can recharge them anytime.  Unlike the old NiCads, they are not affected by being recharged before being run to near dead.  So if you're going to pull them out to test them, might as well recharge.  I have 6 sets of AAA rechargeable for my 4 DCS remotes. Then the battery warning comes up, I pop in a recharged set, put the dying ones on the charger, and resume operations.

Stan ,Thanks for such a detailed explanation ,i have had AAA rechargeable 's in my tv remote since November27 ,& they are still going strong ,i am constantly flipping through channels & changing volumes ,so it gets a lot of use ,so i don't know why my keyboard gets run down so fast ,right now i have duracell batteries in my keyboard since Feb . 21 i want to see how long they last ,i used to get 2 to 3 months use out of the Duracell batteries before i decided to switch to rechargeables . Charlie had a simple solution ,use the rechargeables until the keyboard doesn't work right ,then take them out & recharge them ,thats what i will do for now .As long as i have these batteries i will keep recharging them until they need to be replaced . All great advice ,thanks everyone for your help.