Battery Tester Recommendations - SLA / AGM

[Factotum]

Hey there everyone.

It seems I am surrounded by a lot of repairs involving batteries of late (UPS, solar, etc.)

Mostly small SLA batteries in the 7-12Ah on a regular basis although I do occasionally look at ~200Ah units in solar / inverter rigs.

I'm looking for a tester to check basic faults (go, no go) and lifespan.

The local battery people seem to use a myriad of different units.

I know the price ranges from $600-6000 depending on what features / chemistries they can do.

Any recommendations?

Cheers, Anton.

[Gregg]

For lead acid batteries, there is no substitute for a load test.  Testing the internal resistance will tell you if it definitely is bad, but not how good it may be or how long it may last (no matter what the marketing people tell you).  That is my opinion from over 20 years’ experience with lead acid batteries in telco and data centers.  Management was sold on Midtronics brand testing only to have numerous failures of batteries that tested good and losses of revenue far exceeding the advertised cost savings from the tester's manufacturer. 

There are a number of graphs for load values at given amp hour ratings and temperatures available on the internet, but try to find this information from the battery manufacturer if possible. 
It is surprising the number of lead acid cells that will hold voltage under no load or very light load but fail immediately under moderate or heavy load.

Google “coup de fouet” for interesting LA battery discharge characteristics.

[tautech]

Would a modern electronic load test give enough info ?
Something like these newfangled ones from Siglent:
https://www.siglentamerica.com/dc-electronic-load/sdl1000x/

[windsmurf]

Would a modern electronic load test give enough info ?
Something like these newfangled ones from Siglent:
https://www.siglentamerica.com/dc-electronic-load/sdl1000x/

I was wondering just this... but maybe 300W load isn't enough to test an auto battery?

[tautech]

Would a modern electronic load test give enough info ?
Something like these newfangled ones from Siglent:
https://www.siglentamerica.com/dc-electronic-load/sdl1000x/

I was wondering just this... but maybe 300W load isn't enough to test an auto battery?

The 300W model will allow 20A current draw tests on a 12V battery where the voltage can then be monitored to check battery performance.

[Gregg]

Automotive cranking LA batteries are designed for short high amperage loads (starter motor etc).  The common device for load testing is a carbon pile resistor; basically a stack of carbon/graphite discs that give lower resistance (higher amperage load) the tighter they are squeezed together.  Carbon pile load testers are obviously short term test devices.  It has been a while since I had occasion to use one, but for a ballpark test of a cranking battery rated at 600 to 800 cold cranking amps, a load of 200 amps for 2 minutes will tell a lot about the health of the battery; the voltage shouldn’t fall below about 10V in those 2 minutes.  A discharge that brings any cell below 1.75 may cause loss of capacity, below 1.5 volts per cell may cause permanent irreversible damage.

UPS and other long discharge designed LA batteries are usually rated for a given number of amp hours over a given time.  These require longer load test times at much lower current settings.  An electronic load bank would probably be able to test the smaller of these batteries and test procedure should be available from the manufacturer.

Another reasonable test is to charge up a battery and then leave it sit for a week disconnected; then read the open circuit voltage.  The open circuit voltage depends on the plate chemistry, plate structure, electrolyte density and temperature.  2.25 volts per cell is more or less nominal for a good LA battery open circuit. 

One of the best tests for LA batteries is the % of sulfuric acid in the electrolyte; like the old school hydrometers.  There are refractometers that are calibrated to measure this that are very accurate and use only a tiny drop of electrolyte.  (Less holes in clothes from acid spatter) but using this method on sealed batteries is less than optimal.