Wire three 12V batteries in series to create a dependable 36V pack for your golf cart. This concise guide covers wiring steps, tools, safety checks, and pro tips.

Quick answer

To wire three 12V batteries for a 36V system, connect them in series: join the positive of Battery 1 to the negative of Battery 2, and the positive of Battery 2 to the negative of Battery 3. The remaining free posts are your 36V outputs: Battery 1 (−) is pack negative and Battery 3 (+) is pack positive. Use batteries with the same voltage and capacity (ideally same brand, age, and chemistry).

What you’ll need

• Three matching 12V batteries (lead-acid, AGM, or lithium—same chemistry/capacity).
• Series jumpers and main cables (follow the cart manufacturer’s gauge; many use 4 AWG or 2 AWG).
• Quality copper lugs, heat-shrink, terminal boots, and a proper crimping tool.
• Main fuse or breaker near pack positive sized for your controller/solenoid.
• Multimeter, zip ties, battery hold-downs, corrosion inhibitor, and PPE (gloves/eye protection).

Step-by-step wiring guide

1. Plan the layout. Arrange the three batteries so jumpers are short, direct, and free from sharp bends. Label them B1, B2, and B3 left to right.
2. Power down safely. Remove the key, open any master switch, and disconnect the old pack negative first, then positive.
3. Prep terminals. Clean posts and lugs until bright metal; pre-crimp lugs and slide heat-shrink onto cables before crimping.
4. Make the series links.
   • Connect B1 (+) → B2 (−).
   • Connect B2 (+) → B3 (−).

   Now only B1 (−) and B3 (+) remain free; these become your 36V outputs.

5. Install the main fuse/breaker. Mount it within a few inches of B3 (+) to protect the entire system from shorts.
6. Connect the cart leads.
   • Cart/controller positive → fuse/breaker → B3 (+).
   • Cart/controller negative → B1 (−).

   Route cables away from sharp edges, heat, and moving parts; secure with clamps or zip ties.

7. Verify with a multimeter. Measure across B1 (−) and B3 (+); you should see ~36V (fully charged lead-acid may read ~37–38V at rest).
8. Finish & secure. Fit terminal covers, apply corrosion inhibitor to lead posts, torque lugs to spec, and lock down the battery hold-downs.
9. Test run. With wheels off the ground, power up, listen for anomalies, and recheck for warm cables after a brief throttle test.

Important considerations

• Match batteries. Mixing ages, capacities, or chemistries creates imbalance; the weakest unit limits the pack and fails early.
• Cable gauge matters. Undersized or oxidized cables waste power and overheat; use quality copper and tight, clean terminations.
• Protection is essential. A correctly sized main fuse/breaker near B3 (+) is your last line of defense—never omit it.
• Charging. Use a 36V charger that matches your chemistry. Lead-acid may need periodic equalization; lithium requires a compatible BMS/charger.
• Balancing. Lead-acid packs benefit from occasional individual top-off charging; lithium relies on BMS balancing.
• Ventilation & safety. Lead-acid can vent hydrogen; keep the compartment ventilated and avoid sparks or open flames.
• Maintenance routine. Monthly: check torque, cleanliness, cable integrity, and (for flooded lead-acid) electrolyte levels with distilled water.
• Polarity discipline. Double-check every jumper path before attaching the cart leads. Reverse polarity can instantly damage the controller.

Series vs. parallel (why series is required)

Series wiring adds voltage while preserving amp-hours. Three 12V, 100Ah batteries in series yield a 36V, 100Ah pack—exactly what a 36V cart needs. Parallel wiring would keep 12V but raise Ah, which won’t power a 36V system.

Troubleshooting tips

• No or low voltage: Confirm the two series jumpers are correct; measure each battery (~12–13V). A dead unit drags down the whole pack.
• Jerky motion or dropouts: Check for loose lugs or a weak battery under load. Observe voltage sag while accelerating.
• Uneven charge: Verify charger profile and connectors; balance charge or replace mismatched batteries.
• Hot cables: Indicates loose connections, corrosion, or too-small gauge. Fix immediately.

At-a-glance schematic (text)

B1 (–) —— pack negative to cart
B1 (+) —— jumper —— B2 (–)
B2 (+) —— jumper —— B3 (–)
B3 (+) —— fuse/breaker —— pack positive to cart

Final checklist

1. All three batteries are identical in voltage, chemistry, capacity, and similar age.
2. Series links: B1(+)→B2(−), B2(+)→B3(−); pack outputs: B1(−) and B3(+).
3. Main fuse/breaker close to B3(+); correct-gauge cables; neat, secure routing.
4. Measured ~36V across B1(−) and B3(+); charger matches 36V and chemistry.
5. Terminals covered, pack restrained, compartment ventilated; first run tested safely.

Bottom line

Wiring three 12V batteries in series is straightforward: make two short jumpers to form the chain, connect the cart leads to B1(−) and B3(+), and protect the system with a main fuse. With matched batteries, proper cable gauge, and a compatible 36V charger, your 36V golf cart will run efficiently and reliably.