07 ST 2+2 Electrical issues

[Heyitsme55]

Looking for some help and/or insight. I Been having electrical issues with a 2007 ezgo st sport 2+2 cart. 36 volt system with an Alltrax AXE-4844 400 amp controller. All the wires are 4 awg and have good terminals/connections with no corrosion on any of them.

I thought I had battery issues when I noticed the cart would struggle on inclines. I could drive the cart for 8-10 miles and still have 3 bars on the stock battery gauge (I never thought to check the voltage with a dvm after making a long ride like that)

So I started checking battery voltages. The chart I've added shows the voltage at each battery at 50% charge (according to the stock dash meter) and 100% charge (taken 1 hr after the charger switched off) the stationary voltage is obviously at rest and the loaded voltage is on the steep incline (I've seen other stock carts make this climb with ease) the "total" at the bottom is simply the voltages added up.

All of the voltages are taken with throttle 100% pressed and after the voltage settles down and becomes stable.

I bought the cart used so I'm not sure how far from stock it is. I have replaced what I'm pretty sure was 6awg wires to 4awg connected to the motor. I assume the controller is not stock. I believe the F/R switch is stock.

If there is any other info I can get I'll be happy to get it. I'm just not sure what else will be helpful.

[Heyitsme55]

I don't want to just throw new batteries on the cart if the batteries are not the problem. They are only 2 years old. I feel like the individual battery voltage is good under load which is why I lean towards there being other issue.
Any help would be greatly appreciated.

[JohnnieB]

You do have an aftermarket controller. The stock controller was a Curtis 1206 with a 275A throughput, the 400A AXE is an improvement.

Attached are a few things that may be helpful.

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The bar graph type gauges are notoriously inaccurate, so install a DVM type meter to monitor battery SoC (State of Charge).

The batteries ought to be charged after each use, or at least each night if cart has been used during that day.

Never allow batteries to discharge more the 50% SoC. Attached is a SoC chart for converting voltage to % SoC. It is for Trojan brand batteries, if you have different brand, a diffe4rent chart may be needed.

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If any cable, contact or connection is getting hot, it needs to be fixed.

The F/R switch contacts are likely suspects.

[JohnnieB]

Took look at your battery chart. Dropping from 38.2V down to 27.5V under load indicates one of two things.
1. Bad amp source (Batteries)
2. Bad amp delivery system. (Cables, connection and contacts)
OR a combination thereof.

The sum of the individual battery voltages under load being higher than the battery pack voltage under load points to bad cables/connection/contacts, but unless you somehow managed to measure the voltage of each battery while climbing the hill, the readings may be skewed by the battery voltage recovery rate.

Again heat is the tattle-tale. Check the temperature of the cable and cable ends and F/R studs. None should be more than about 10°F above ambient.

[Heyitsme55]

checking the voltage while driving uphill all in 1 shot would have been a neat trick having to move the alligator clips from battery to battery under the seat. Unfortunately it took 6 passes up the same hill with my 8 year old logging the data from the dvm.
Thanks for the info, I will make the hill climb then immediately check the temps after work and hopefully have some smoking gun results to respond with.