A recent comment that I received reminded me that I had never really discussed how to test for a bad battery in a gas golf cart. I go into a lengthy discussion of battery testing in the “Electric Cart Stuff” section, but there is nothing there about a gas cart’s battery. So, here it is.
First off, it is important to understand that the battery used in a gas golf cart is a totally different “critter” than the one used in an electric cart (or at least it is supposed to be). The battery in the gas cart is more like a battery used in an automobile. It is a 12 volt (we’ll get into that in more detail in just a moment) and it relies on Cold Cranking Amperage (CCA) to have enough energy to spin the engine over long enough to get it started. Once the engine is started, the battery has done its job and the rest is up to the starter/generator (S/G). The S/G supplies a charge voltage, controlled by the voltage regulator (VR) to recharge the battery as the engine runs. The battery, at that point, acts as what I call a ballast. It can still supply short term energy to anything that might require more than the S/G can handle for short periods of time, but basically it just sits there RECEIVING energy from the charging system to maintain its proper charge. It is not intended (like electric cart’s battery) to supply a constant source of energy for anything for a long period of time.
Let’s talk about a “so called” 12-volt battery. Batteries are made up by connecting (within the battery package) what we call 2-volt cells in series, to add up to the total battery’s rated voltage. In our case, it takes three 2-volt cells connected in series to add up to the 12 volt rating of the battery.
However, a 2-volt cell really isn’t a 2-volt cell while it is usable. A 2-volt cell, when fully charged, ideally measures about 2.15 volts. By the time it has discharged down to 2 volts, it is nearly useless, and needs to be recharged. So, our 12-volt battery, being made up of three 2-volt cells should measure about 12.9 volts when properly charged. That is (in battery language) a far cry from 12 volts.
So, if your S/G and VR are doing their jobs, when you walk up to the golf cart, lift the seat and put a meter across your battery, it should measure about 12.9 volts. As the battery ages, its ability to come back up to a full charge lessens, so if your battery has a few years on it, you might measure closer to 12.75 or so, but should be considerably higher than 12 volts.
Now the question comes up: what happens to the voltage of the battery when you hit the accelerator to start the engine? Answering that question is an excellent way to “load test” the battery. Leave the meter across the battery and watch it as you try to start the engine. Under no circumstances should the voltage drop below around 11 volts while starting the engine. For an older battery, it might still work if it goes as low as 10.5 volts, but it should never go any lower than that. Of course, as soon as the engine fires, the generator function of the S/G should kick in under the supervision of the VR and start recharging the battery, so you should see the voltage at the battery crawl back up to the 12.9 volts right away and then go on up higher as the RPM of the engine increases. Ideally, the VR will limit the maximum charging voltage to about 14.5 volts to prevent damage to the battery.
So that is what you should see going on with your meter during the “start-up” process. What could possibly go wrong? Lots of stuff.
Let’s say that when you lift the seat and do your test with nothing turned on, and the cart is just sitting there, I call this the “static” test of the battery. Let’s say that it only reads 11.6 volts. What we don’t know is “why” at this point. It could be that the battery is bad or that the S/G and VR aren’t recharging it. The best thing to do is to put an automotive charger on the battery overnight and then test it again. If it is up around 12.9 volts, then we will be suspicious of the S/G or VR, but we haven’t proven anything yet. If the static voltage isn’t around 12.9 after the overnight charge, then the battery simply won’t accept a charge and needs to be replaced (assuming the charger is known to be good). The next part of the test is what I call the “dynamic” test where we continue to monitor the meter while we actually try to start the engine. If the voltage doesn’t drop below 11 volts and the engine starts, we will even be MORE suspicious of the S/G and VR. If the voltage drops way below the 11 volts (let’s say 8 volts) then we are back to the battery again. It is quite common for the static volage to come up to something fairly normal after an overnight charge, but the battery doesn’t have the “capacity” to supply the necessary energy for the start-up without dropping the voltage too low to make things work.
So what have we done?
By doing the overnight charge, we have given the battery an opportunity to become properly charged, in case the problem is that the S/G or VR is the problem.
By seeing what happens with the dynamic test, we are doing a GREAT load test of the battery. You can buy a load tester at an automotive supply store, but it isn’t the same as using the actual cart for the test. The cart IS the proper load that the battery should be tested with. A load tester generally only loads the battery to about a 100 amp load. When starting the cart, we can easily exceed that amount. Most of the gas cart’s batteries are rated at least 400 amps CCA, so the external load tester may not test under enough of a load or for long enough to make a good discission about the condition of the battery. Using the cart as our load tester is a far superior method than an external load tester.
If we determine that the problem is the S/G or the VR, then we need to do some procedures to isolate further. Those procedures are described in another page of this website called “E-Z-Go gas cart Starter/Generator and Voltage Regulator” under Gas Cart Stuff in the drop-down menus (E-Z-Go gas cart Starter/Generator and Voltage Regulator – Welcome to Golf Cart Stuff Hodgepodge). Don’t worry about the E-Z-Go part. The procedure is basically the same for all makes and models.
For information about books written by Ron Staley about both electric and gas driven golf carts and their repair, visit the following links.
Electric Golf Cart Repair, both as an eBook and in Hardcopy:
Book: Ronald L Staley: 9780578560557: Amazon.com: Books
Gas Golf Cart Repair, both as an eBook and in Hardcopy:Gas Golf Cart Repair Book: Ron Staley: 9798987911303: Amazon.com: Books