I just received a large shipment of battery backup batteries for the numerous battery backup devices I have.
Most of them are 12v and around 7 - 8Ah but some are larger.

I'm mostly concerned about the 7-8Ah batteries.

I know there are commercial load testers available, but I don't trust them too much after reading all I could.

What I would like to do is rig up a home made load tester using a known load.
Let's say a load of somewhere around 5 - 8 amps. That's easy to do with a headlight bulb for example.
So in this example, let's say I have a headlight bulb that draws a known current of 6.3amps (because that's what I have)

The load test in basic terms will answer the question: How long can this 7.2Ah battery run a 6.3A bulb?

Until it dims? That's not very scientific. So what I'm asking is, what would be the right way to administer this load test?
Would I run the bulb until the battery amps drop below a certain amperage or would I run the bulb until the VOLTAGE drops below a specific voltage?..and for a 12v, 7.2Ah, AGM battery how would I know what that voltage (or current) is?

Thanks

 

Calculations show 1.hour 8 mins, that would probably be until the battery drops to 11v or less.

 

I just received a large shipment of battery backup batteries for the numerous battery backup devices I have.
Most of them are 12v and around 7 - 8Ah but some are larger.

I'm mostly concerned about the 7-8Ah batteries.

I know there are commercial load testers available, but I don't trust them too much after reading all I could.

What I would like to do is rig up a home made load tester using a known load.
Let's say a load of somewhere around 5 - 8 amps. That's easy to do with a headlight bulb for example.
So in this example, let's say I have a headlight bulb that draws a known current of 6.3amps (because that's what I have)

The load test in basic terms will answer the question: How long can this 7.2Ah battery run a 6.3A bulb?

Until it dims? That's not very scientific. So what I'm asking is, what would be the right way to administer this load test?
Would I run the bulb until the battery amps drop below a certain amperage or would I run the bulb until the VOLTAGE drops below a specific voltage?..and for a 12v, 7.2Ah, AGM battery how would I know what that voltage (or current) is?

Thanks

Motorcycles with electric start usually have a battery somewhere between 9 - 15Ah
I routinely used the starter on a small motorcycle to check UPS batteries.

Some UPS boxes refused to run even though the battery passed the usual tests - the motorcycle starter was sluggish and pointed out the dodgy batteries.

Don't worry about stressing a 7Ah battery on a 9Ah motorcycle - I've got away with 10x 4Ah D-cell Ni-Cd acouple of times.