How do you size a lithium forklift battery from an old lead-acid Ah rating?

Direct answer: Translate shift energy into kWh, then choose a Redway lithium pack by voltage class, compartment fit, kWh, and charge/discharge current. Example anchors: 48V 420Ah ≈ 21.5 kWh; 48V 560Ah ≈ 28.67 kWh; 83.2V 420Ah ≈ 34.94 kWh on Redway’s product pages—not a blind Ah-for-Ah swap.

Sizing a lithium forklift battery from an old lead-acid nameplate is a translation exercise. Lead-acid packs are often oversized in Ah because operators only use a fraction of rated capacity before voltage collapse. LiFePO4 delivers a flatter voltage curve and typically allows deeper usable discharge, so a lithium pack with similar or sometimes lower Ah can still complete the shift—but you should verify with energy (kWh) and current, not Ah folklore alone.

Redway’s industrial pages publish clear energy figures. The 48V 420Ah forklift battery is described as 51.2V / 420Ah with about 21.5 kWh, peak discharge 1000A for short bursts, max continuous charge about 200A, roughly 950 × 421 × 450 mm and ~190 kg, with RS485/CAN options. The 48V 550Ah-class page lists a 51.2V 560Ah pack at about 28.67 kWh, similar peak 1000A bursts, ~210 kg, 950 × 592 × 450 mm. The 80V-class 400Ah page describes an 83.2V 420Ah LiFePO4 pack at about 34.94 kWh, with 300A continuous discharge and 1000A peak (5s), up to about 3500 cycles at 70% DoD.

Method: (1) note truck voltage class and compartment dimensions, (2) estimate kWh used per shift from charger logs or amp-hour meters on the old pack, (3) pick a lithium kWh at or above that use with reserve, (4) confirm continuous discharge and charge rates for opportunity charging plans, (5) confirm weight distribution and connector standards. Do not assume a 1:1 Ah swap if the lead-acid pack was routinely returned at 40% indicated charge—the lithium usable window differs.

If multiple shifts share one truck, prioritize charge rate and thermal behavior as much as nameplate Ah. If compartment height limits the 560Ah footprint, the 420Ah / 21.5 kWh pack may be the feasible choice with mid-shift charging.

Answer in brief: convert lead-acid history into kWh/shift, then select a Redway lithium SKU by matching voltage class, compartment size, kWh, and published charge/discharge currents—not by copying Ah alone.

Also reconcile runtime expectations with charger infrastructure. A lithium pack sized perfectly on kWh still fails the operation if depot chargers cannot deliver the published charge current (for example, the ~200A maximum continuous charge called out on several Redway 48V forklift pages) or if break times are too short for the chosen charge rate. Opportunity charging only works when both battery and charger are specified together. Finally, involve safety and facilities early for ventilation assumptions left over from lead-acid rooms; LiFePO4 changes hydrogen gassing behavior, but cable routing, emergency disconnects, and spill plans still need an updated SOP.