How to test auxiliary batteries for amperage?

Other than an inverter, I can't either.

Inverter load, starter motor engine disabled.

Wluldn't an accurate hydrometer reading work?

Just like testing a 12 volt battery. A giant resistor, a period of time to apply the load, and a way to read the voltage. Oh thats right, its called a load tester.

Capt. Obvious might be on to something there.

Hygrometer isn't going to read out damage to the plates.

Go to Advance / Autozone and rent their battery load tester. It's just a box with a big resistor and a meter, should be cheap / free with a deposit.

GordonThree wrote:
Hygrometer isn't going to read out damage to the plates.

Go to Advance / Autozone and rent their battery load tester. It's just a box with a big resistor and a meter, should be cheap / free with a deposit.

Or better yet, take the batteries to one of those places and ask them to test them. They will put them on a tester and run the test for you for free. Of course, they do this because they want to sell you a new battery, but not being able to do so because the problem is really elsewhere, but they are friendly and helpful none the less.

guess its a matter of moving 200lbs of batteries or a 40lb tester :) either way works

Hydrometer.

Get a load tester.

Usually the Interstate battery Distributors have an 800-amp Auto Meter adjustable carbon pile load tester. The distributor. The guy with the trucks.

Harbor Fright sells 500 amp adjustable carbon pile testers.

NiChrome wire was killer expensive back in the early eighties. I shudder to think what 10-gauge costs now. Then it has to be spiraled ultra slowly on a lathe jig. I used 4x8 sheets of linen bakelite for load bank platforms. Yuk.