testing deep draw batteries

[KarlP]

I work at a place that accepts donated Power Wheelchairs,  They usually contain two deep draw batteries, one of which has died, and the other of which may still be alive.  I use an automotive charger to desulfate and charge them, but need a way to draw them down and them put them back  on the charger through several cycles.  My boss will not let me use them unless there is some way to be sure that they will not die quickly and leave some poor person stranded.

To me that suggests some sort of dummy load that can handle DC 12v at 10 amps or higher. (Some of these batteries are rated at 160AHrs)

If such a device exists, I am having no luck in finding it.

Any suggestions appreciated

[RoGeorge]

I would use a few of 12V incandescent auto headlight bulbs in parallel.

[macboy]

Look at R/C battery chargers. Normally these are used with lithium batteries, but most have the ability to charge and discharge lead batteries as well. All will measure the capacity when discharging and charging. Many will discharge into an external load resistor at very high power (>>100 watt).  Some do regenerative discharge, where the power source is a battery (higher capacity than the battery being charged/discharged/cycled), and the discharge power is put back into that source battery rather than wasted as heat. On my chargers, I can set it up to cycle the battery N times and it will repeatedly charge and discharge, keeping track of the mAh into and out of the battery each time. If the power source is a large Pb battery (e.g. car battery) then this process generates little heat and wastes little power.  One of my chargers will discharge at up to 18A into a suitable load resistor or battery, and some are much more powerful than mine.

[electr_peter]

Search for "electronic DC load" - these are useful in discharging batteries at various levels and logging voltage drop/Ah/Wh.
However, in my experience, lead acid batteries age and die, there is not much to be done to bring them back to service.

[Stray Electron]

  I would suggest trying one of the battery tender chargers and seeing how that works.  I have several of them and they will all tell you the state of the charge of the battery when you connect them, and then show you the state of the charge (% of capacity) as they charge, and will then show you and battery capacity when the finish.  They're fully automatic and you can connect them and then just leave them alone and let them do their job.  Come back a day or so later and see what they report.

   This is the one that I've used the most https://www.amazon.com/Schumacher-SP1297-Automatic-Battery-Maintainer/dp/B0756PV96N

   One of the nice features of this model is that the outlet cord has a 2 pin plastic plug on it and the charger comes with two different ends for the cord.  One cord has ring terminals so it can be semi-permanently attached to a battery and then the cord just plugged in when needed. (See picture #3.) Or the other end has the usual crocodile clips (picture #1).  One of my cars (a MB) doesn't get driven very often and this model is notorious for running down batteries and then having serious issues, so I attached a cord to one of the two batteries in the car and the plug is located in the trunk. Now all I have to do is to open the trunk and plug in the maintainer and I can leave the car for as long as I want and not have to worry about what happens to the battery. 

   Once you have fully charged the battery then you can do as RoGeorge suggested and just use a couple of automobile headlights to load test it. Connect up as many lamps as you need and let them run for say an hour and then disconnect the lamps and reconnect the battery tender and see what the battery state is. If it's lower than expected or if the battery fails to charge initially then you know that it's bad. 

   FYI I think that most of those powered wheel chairs run their batteries in series. If so then I don't think that you're going to find many where only one battery is bad.  My mother worked in her church's thrift store and they had many powered chairs given to them after the owner died.  But I don't think that they ever got one that had any good batteries.  Many had not been used much when the owner was alive (many were so disabled that they couldn't get in and out of the chair by themselves) and they also hadn't been recharged regularly so that would kill the batteries even when the owner was living. But also after the owner's died, the chairs would sit around for many months, and sometimes years, without being recharged (and usually the charger was lost) before the family or the estate donated the chair to a charity. So again the batteries were ruined.

[KarlP]

Thank You for the comments.  I am going to hit a junk yard and get a few headlights for my load.  My first batch of  Chairs to process was 14 chairs, and even though they are wired to produce 24 v.  When I hooked up my 12 V charger on the individual cells, it de-sulphated them, then charged them.  Usually one of the batteries from a chair was bad and the other took a full charge.  Before i put them into a chair, I need them to go through several full discharge cyclesto I just counted them and I have 14 to cycle test.

[donlisms]

I don’t know anything about anything, but it occurred to me that they might use a simple series connection to get the 24 volts.  There wouldn’t be any balancing between the batteries - one wins while the other looses.  Somehow.

[Conrad Hoffman]

De-sulphating lead-acid batteries is mostly a wish and a myth, but sometimes you get lucky. I'd want to see several healthy charge/discharge cycles plus a longer term test to be sure they hold their charge for the expected amount of time.