Replacing Lead-Acid with Lithium: A Practical Checklist

Measure first: compartment, terminals, cable reach

A lead-acid replacement checklist starts with the space the old battery occupies, not with the battery you plan to order. Measure the compartment's internal length, width and height at the tightest points, including any lip, hold-down bar or lid that closes over the top. Record terminal position, terminal type and the direction the cables leave the posts.

Cable reach decides whether a drop-in format is even possible. Lithium packs often sit lower or shorter than the flooded or AGM block they replace, so the positive and negative leads may no longer reach the posts without strain. Note the cable length available with the bank removed and confirm there is slack to route around a different terminal layout.

Finish the measurement pass with the mounting method. Record how the existing bank is clamped, because the replacement needs its own hold-down that matches its case. A pack that fits the cavity but cannot be secured is not a fit. Bring these measurements to the specification stage; fit is confirmed per model against your actual compartment, not against a generic size class.

If the application is a counterbalance truck, the same measurements apply but the compartment constraints are tighter and the counterweight calculation enters earlier. The measurement sheet you build here feeds directly into the specification for forklift lithium batteries and for any other vehicle class you are converting.

Match the system voltage and capacity class

Voltage is the first hard constraint. Count the series cells or blocks in the existing bank and confirm the nominal class it operates at, whether that is a 12V or 24V system or a higher-voltage arrangement built from those blocks. The replacement must present the same nominal class to the vehicle's controls, contactors and DC-DC converters, because those devices are designed around a fixed input range.

Capacity needs a more careful reading than the label on the old block. A lead-acid rating is usually quoted at a slow discharge rate, and only part of that quoted capacity is available in real service before voltage sags under load. A lithium pack delivers close to its rated capacity across the discharge, so the class you choose is not a like-for-like copy of the lead-acid number. Compare the old block's usable capacity against your actual duty cycle, not its printed rating.

Our replacement approach uses LiFePO4 units in 12V/24V documented classes. That chemistry holds a flatter voltage curve through the discharge, which affects how the vehicle's state-of-charge indication behaves and how the low-voltage cut-off is set — both covered below. The same class logic applies across the lead-acid replacement batteries range, and the LiFePO4 batteries page explains the cell-level behaviour behind it.

Confirm the parallel arrangement as well. If the old bank used two blocks in parallel to reach the required capacity, decide whether the replacement keeps that split or consolidates into one pack. Both are workable; the choice changes cable routing, hold-down design and how the BMS reports each unit.

Check the charger before anything ships

The charger is the most common reason a conversion disappoints, so it belongs in the checklist before the purchase order, not after delivery. Lead-acid chargers run multi-stage profiles with a long absorption phase and often a float stage, and those stages assume the voltage behaviour of a flooded or AGM block. A lithium pack needs a different charge profile, and an incompatible charger can leave the pack partially charged or push it outside its safe window.

Charger compatibility must be checked per project. Send the charger model, its output voltage and its charge profile to the specification stage, and confirm the settings can be adjusted or that a suitable charger is part of the project. Do not assume a charger that worked on the old bank will work unchanged on the new one.

Check the charge source in every mode the vehicle uses. Opportunity charging during breaks, overnight charging and any onboard charger each present their own profile, and all of them must be confirmed. If the vehicle has a battery management system that talks to the charger, confirm the communication protocol matches.

Document the agreed charge settings in the project specification. Options are confirmed in the project specification; not every model carries every option, and the charger arrangement is one of them. A charger confirmed at the start removes the most common cause of a returned pack.

Weight change and ballast planning

Lithium packs weigh less than the lead-acid blocks they replace, and on most vehicles that is an advantage: less mass to accelerate, less load on the tyres and floor, easier handling during a swap. On a counterbalance forklift it is a design problem, because the battery itself is part of the counterweight that keeps the truck stable when it lifts a load at height.

Plan the ballast before the pack is ordered. Establish the truck's rated capacity and the counterweight contribution of the old bank, then decide how the missing mass is replaced — usually with a ballast block in the compartment or a modified counterweight. The goal is to restore the stability margin the truck was designed around, not to match the old weight exactly for its own sake.

Ballast planning also affects the compartment. A ballast block needs its own hold-down, and it changes the space left for the pack and the cable routing. Work the two together rather than treating ballast as an afterthought once the pack dimensions are fixed.

Keep a record of the ballast change with the vehicle documentation. Inspectors and service technicians need to know the truck no longer carries its original battery mass, and a written record prevents a later swap back to lead-acid from being done without recalculating stability.

BMS behaviour: low-voltage cut-off and alarms

A lithium pack protects itself through its battery management system, and that changes how the vehicle behaves near the end of discharge. A lead-acid bank sags gradually and gives the operator warning through sluggish lifting or dim lights. A lithium BMS instead cuts off at a set low-voltage threshold, and the cut-off is sudden: the vehicle stops rather than fading.

Set the cut-off threshold with the vehicle's own low-voltage protection in mind. If both the BMS and the vehicle controller try to protect the same circuit, decide which one acts first and confirm the settings do not fight each other. A pack that disconnects while the controller is still demanding current can trip contactors or log faults.

Alarms need to be visible and audible to the operator before the cut-off. Confirm how the BMS reports low state of charge, over-temperature and any cell-level fault, and where that signal appears — a dashboard indicator, a buzzer, or a data link to the vehicle controller. An alarm nobody hears is not a protection feature.

Decide what happens after a cut-off. Some BMS designs latch off and need a charger connection or a reset signal to recover; others reclose automatically once the cells recover. Tell the operators which behaviour to expect, because a latched pack on a shift-change can look like a failure when it is normal protection.

Disposal and documentation for the old bank

The old lead-acid bank is hazardous waste and must leave the site through a proper route. Lead-acid batteries are collected and recycled through established channels in most markets, and the disposal paperwork often needs to be retained. Arrange collection before the new pack is installed so the old bank does not sit unsecured in a yard.

Check the local rules for transport and storage of the removed bank. A discharged lead-acid block is still regulated waste, and storing it indoors or near drains may be restricted. Confirm whether your site needs a waste transfer note or an equivalent record, and keep the collection receipt.

Build a documentation file for the conversion as a whole. It should hold the measurement sheet, the confirmed voltage and capacity class, the charger settings agreement, the ballast record and the disposal paperwork for the old bank. That file answers the questions a service technician, insurer or auditor will ask later, and it makes a future replacement straightforward.

Documentation also covers the new pack itself. Certification claims are made per model: ISO 9001 and ISO 14001 certified manufacturing sits behind the build, and UN38.3, IEC 62133 and MSDS documents can be confirmed and provided for specific models — tell us the model you are buying and we will confirm which documents cover it. Keep those documents with the vehicle file rather than in a project folder someone else owns.

Finally, record the configuration of the new pack — series and parallel arrangement, BMS settings and charge profile — next to the disposal record for the old one. The pair of records turns a one-off conversion into a repeatable procedure for the rest of the fleet.