Hi I own a lead acid battery restoration company and have been receiving more big business customers lately. To keep up with this demand, I'd like to build a portable tester that can use to test their batteries on site before I transfer them to my workshop. I need the tester to forcefully push 48v through the batteries I want to test so I can pop the caps off and see if any oxygen/hydrogen bubbles are forming and if they are, I'll know the battery's internals are still in tact.

Would it be possible to build a 48v bank of 18650 batteries and then have some sort of isolation circuit that will only transfer the energy one way from the bank to the battery to be tested?

 

This has the potential to be pretty scary so safety is a primary concern.

48V but how many amps?

Four those LiPo based jump starters might be a good basis for your device? This one, for example. From what I know, they are basically just big LiPo cells wired up to 12V with some big diodes to prevent current from coming back into the pack from the alternator.

Still, the prospect of a bunch of LiPo cells with that much energy in them all in one place... It makes me nervous.

It you don't need super high current then can you work with a higher voltage? If so, 18V tool batteries, 3 in a series, gets you 54V pretty cheap. If you had to have exactly 48V then you could use a buck converter with the batteries. But the higher the current the less attractive this idea becomes. So, the total current you need makes a big difference.

 

just in case The Differences Between AGM, GEL and FLOODED Batteries

 

Looking for Bubbles is not a good way to judge the health of Lead-Acid-Battery.
That's Hydrogen-Gas coming out of those Batteries, and it's explosive, and you'll be making SPARKS.
Not a good combination.

A DC "Amp-Clamp" and a Volt-Meter is all You need,
( preferably with a "Hold" feature on each ).

The Starter provides a serious Load, and is already attached to the Batteries.

A Voltage verses Current Chart is the only other thing You'll need,
unless you're in an environment with temperature extremes,
then having a Temperature compensation Chart would come in handy.

Have the Driver of the Truck operate the Starter, with the Fuel shut-off.
Only the Driver is qualified to operate anything on the Truck.

The Battery-Terminals, as well as any "Jumper-Cables" between Batteries, ( if used ),
are just as important as the internal condition of the Batteries.
.
.
.

 

Testing battery health is a multi-facetted problem. For instance, batteries which show good terminal voltage could have high resistance cell interconnects. A battery with a shorted cell can still give good discharge current.
https://www.durite.co.uk/s/c/batter...nance/battery-testers/durite-discharge-tester
has been doing an adequate job for years

 

Thank you everyone for the valuable info.

Looking for Bubbles is not a good way to judge the health of Lead-Acid-Battery.
That's Hydrogen-Gas coming out of those Batteries, and it's explosive, and you'll be making SPARKS.
Not a good combination.

A DC "Amp-Clamp" and a Volt-Meter is all You need,
( preferably with a "Hold" feature on each ).

The Starter provides a serious Load, and is already attached to the Batteries.

A Voltage verses Current Chart is the only other thing You'll need,
unless you're in an environment with temperature extremes,
then having a Temperature compensation Chart would come in handy.

Have the Driver of the Truck operate the Starter, with the Fuel shut-off.
Only the Driver is qualified to operate anything on the Truck.

The Battery-Terminals, as well as any "Jumper-Cables" between Batteries, ( if used ),
are just as important as the internal condition of the Batteries.
.
.
.

You're absolutely right that sparks + hydrogen = boom. I've been doing battery reconditioning for a long time using electrolysis, so I'm very much aware of the dangers. That said, I only test batteries once they've been removed and I'd have a switch to block current from going to the battery until after I attach the clamps. That way, the terminals won't spark.

This has the potential to be pretty scary so safety is a primary concern.

48V but how many amps?

Four those LiPo based jump starters might be a good basis for your device? This one, for example. From what I know, they are basically just big LiPo cells wired up to 12V with some big diodes to prevent current from coming back into the pack from the alternator.

Still, the prospect of a bunch of LiPo cells with that much energy in them all in one place... It makes me nervous.

It you don't need super high current then can you work with a higher voltage? If so, 18V tool batteries, 3 in a series, gets you 54V pretty cheap. If you had to have exactly 48V then you could use a buck converter with the batteries. But the higher the current the less attractive this idea becomes. So, the total current you need makes a big difference.

High current isn't required to initiate electrolysis within a lead acid battery. Even 10 amps is sufficient. The reason I need higher voltage is because sometimes the lead plates become heavily sulfated and require a strong voltage to break through the barrier.

Now that I think about it, DeWalt 60v max batteries also have a 20v mode, so maybe I could utilize that and have a way to switch between those two modes?

Testing battery health is a multi-facetted problem. For instance, batteries which show good terminal voltage could have high resistance cell interconnects. A battery with a shorted cell can still give good discharge current.
https://www.durite.co.uk/s/c/batter...nance/battery-testers/durite-discharge-tester
has been doing an adequate job for years

You're quite right about this. That's why I pop the caps when I perform the electrolysis. When one or more cells produces "fizzing" rather than large bubbles, that's an indicator that the plates have deteriorated or one or more of the interconnects has become disconnected. In addition, pulling a sample of the electrolyte while electrolysis is happening is a good indicator of how heavily deteriorated the plates have become. That said, I will definitely look into this device you linked. If I can get an in depth, professional battery tester, that would certainly be more attractive than something I slap together.