Why does a lithium golf cart battery read lower voltage under acceleration?

Direct answer: Some voltage drop under load is normal for any battery. Current flowing through the pack’s internal resistance, the cables and the connections lowers the voltage the controller sees, and the drop grows with current, low charge and cold. It is a concern when the drop is large, keeps getting worse, triggers BMS cut-outs, or comes with hot cables or terminals. Measure at rest and under load at the battery and at the controller to find where the drop happens.

How big can normal sag be? The 48V 100Ah golf cart battery page lists internal resistance below 10 mΩ. Our arithmetic: at 200A, its 10-second peak, 0.01 Ω × 200A gives up to 2V across the battery itself. Cables and connections add their own drop on top. A few volts at full acceleration that recover when you lift off is consistent with that; ten volts is not.

Know the current limits. The standard 48V 100Ah page lists 100A continuous and 200A peak for 10s; the high-current version lists 230A continuous and 250A for 10s; the Redway 48V 100Ah (model with 300A peak) lists 100A continuous and 300A for 20s. If the motor controller asks for more current than the pack allows for longer than the peak time, the BMS may cut power. That is a sizing issue, not a fault; see standard vs high-current packs.

Other causes. State of charge: voltage under load is lower near empty. Temperature: cold raises internal resistance, so sag is larger on cold mornings. Connections: a loose or corroded lug or an undersized cable adds resistance exactly where it is hard to see.

How to measure. With the cart parked, note the pack voltage at the battery terminals. Then, with the cart safely lifted or on a test run with a helper, measure under load at the battery terminals and at the controller input at the same moment. If both drop by a similar amount, the drop is inside or at the battery; if the controller input drops much more, look at the cables, fuse, contactor and lugs between them. Check for warm terminals afterwards.

When to call support: the at-rest voltage is low after a full charge, the drop grows week by week, the BMS cuts out on normal hills, or one pack in a fleet behaves differently from identical carts. Send the readings, the state of charge and the temperature with the serial number.