36 Volt Forklift Batteries: Performance & Maintenance Guide

If you are comparing 36 volt forklift batteries, the truck has already decided the voltage. What is still open is the chemistry, the capacity, the charger, and whether a quoted battery can be documented as a fit for your specific truck. This guide takes those decisions in the order they usually hold up a purchase:

1. What the truck requires
2. How to size capacity and charge time
3. How lead-acid and lithium iron phosphate (LiFePO4) figures should be compared
4. What each chemistry asks of your maintenance team afterwards

Electric forklift operating in a distribution warehouse, where 36 volt battery performance requirements are evaluated.

"36 volt" is a voltage class, not an exact operating voltage. The two chemistries reach it differently:

Other LiFePO4 packs sold for 36V trucks may use a different series count and voltage window, so check the specification of the pack you are quoted. A lithium pack may also contain more cells than its series count, connected in parallel within each series group. What sets the voltage is the number of groups in series.

The difference matters when a lithium pack goes into a truck designed around lead-acid. Our four 36V-class packs, for example, are published at:

• 38.4 V nominal
• 43.8 V charge cut-off
• 33 V discharge cut-off

The truck's controller, discharge indicator and low-voltage settings have to accept that window, including the voltage dips that occur under heavy load. That is a check to make with the truck manufacturer or dealer. The "36V" label does not settle it.

Three things on the truck can rule a battery out regardless of its capacity or price: the data plate, the battery weight, and whether the pack physically fits, mounts and connects.

Data plate

Start with the forklift data plate and the nameplate of the battery currently in the truck. Toyota's explanation of its own data plates shows the kind of information to look for: battery voltage, and the minimum and maximum battery weight the truck is approved for (Toyota Material Handling). Other manufacturers lay their plates out differently, so photograph yours rather than assuming the same fields.

Record the truck model and serial number at the same time. A dealer or battery supplier needs them to look up anything the plate does not show.

Battery weight

On an electric forklift the battery is part of the truck's counterweight. A battery lighter than the data plate minimum can affect rated capacity and stability. That is why weight should be checked before capacity.

The gap between chemistries can be large:

• One US supplier lists a 36 V, 750 Ah lead-acid battery at 2,205 lb, roughly 1,000 kg (M-Pulse Power).
• A 36 V, 690 Ah LiFePO4 pack from another manufacturer is listed at 330 kg, and its spec sheet states that figure excludes counterweight (RoyPow).

These are catalogue values for different capacities, so they show the scale of the difference, not a fixed ratio.

Lithium packs close the gap with ballast. Toyota, for instance, describes its lithium batteries as built with integrated counterweight to meet the truck's weight requirement (Toyota Material Handling).

Weight, counterweight and the data plate

Confirm the installed weight of the exact configuration you are quoting, including any ballast, before you compare it with the data plate range.

Installed weight

Ask for the weight of the configuration being quoted, with and without counterweight. Our four 36V-class models are published at weights between 910 kg and 1,054 kg; treat those as catalogue figures.

Written confirmation

Ask the truck manufacturer or dealer to confirm the weight range in writing before you order.

When you read any lithium spec sheet, ask for the installed weight of the exact configuration being quoted, and whether that figure includes ballast. Then compare it with the minimum and maximum on your data plate.

In the United States there is also a regulatory side. OSHA requires the manufacturer's prior written approval for modifications that affect a truck's capacity and safe operation. It also does not allow additional counterweighting unless the truck manufacturer approves it (OSHA 29 CFR 1910.178). If a replacement battery changes the truck's weight or needs added ballast, raise it with the truck manufacturer or dealer before you order. Operators outside the US should check the equivalent local rules.

A lighter battery does not make a truck more stable. Meeting the data plate weight range is necessary, but it is not the whole fit. The battery also has to be restrained correctly, fit the compartment, place its weight where the truck design expects it, and be accepted by the truck manufacturer or dealer. For more on this, see our article on counterbalance forklift battery sizing and battery weight.

Compartment, mounting and connector

Measure the usable length, width and height of the battery compartment separately. Enclosure shapes vary more than capacity suggests. Among our own four 36V models, the 880 Ah pack is 409 mm wide while the 660 Ah pack is 510 mm wide, and heights run from 570 mm to 787 mm. A higher-capacity pack is not necessarily the larger one in the dimension that limits you.

Then check what surrounds the battery:

• The direction it is removed
• Lifting points
• How it is restrained in the compartment
• Where the cable exits
• Room for the connector and cable bend

Record the truck-side connector model, rating and polarity. Two connectors of the same brand are not automatically compatible.

Ask every supplier for a drawing of the quoted configuration. A catalogue photo of the standard model does not tell you where the cable exits on the pack you will receive.

From amp-hours to energy

Capacity in amp-hours tells you how much charge a battery stores. To compare batteries, convert it to energy:

Energy (kWh) = nominal voltage (V) × capacity (Ah) ÷ 1,000

Two examples:

• A 36 V, 750 Ah lead-acid battery works out to a calculated nominal 27 kWh.
• A 38.4 V, 660 Ah LiFePO4 pack works out to about 25.3 kWh.

Neither number is a runtime. Lead-acid capacity is also rated at a specified discharge rate, so check which rate a nameplate refers to.

Matching energy to your shifts

Usable energy is only part of the answer. The other part is what your trucks actually consume. A workable sizing method:

1. Measure demand. Use discharge records from your current batteries, or a supervised trial, to find energy used on a representative shift and on your heaviest one. Travel distance, lift height and frequency, load and temperature all change it, so a typical-truck figure is no substitute.
2. Set the usable window. Take the depth of discharge (DOD, the share of rated capacity drawn out) that the battery manufacturer allows. Then keep a minimum reserve above the point where the truck or battery management system (BMS) limits performance.
3. Check every shift, not the average. The plan works only if, for each shift: energy used ≤ energy available above your minimum reserve at the start of the shift + energy actually added during breaks. Carry the state of charge (SOC, the percentage of charge remaining) at the end of each shift into the next one. If SOC drifts below your reserve over a week, the plan fails even if one shift looks fine.
4. Allow for cold and ageing. Usable capacity falls in cold conditions and over the battery's life. Ask the supplier how much, under what conditions.
5. Confirm on the truck. Run a trial and read the battery's SOC records before committing a whole fleet.

Estimating charge time

Charge time can be estimated the same way:

Ideal charge time (hours) = amp-hours to be replaced ÷ charge current (A)

The table applies that formula to our published 36V-class specifications for the standard configurations listed.

Specifications are Polinovel manufacturer-stated values. Times and additions are calculated, not measured. They assume the full published current flows for the whole period, so the times are lower bounds and the additions are upper bounds. In practice, current tapers near the end of charge and can be limited by temperature, and plugging in and starting a charge also takes time.

High-capacity LiFePO4 forklift battery pack, sized for charging during operational shift breaks.

Two practical points follow.

Fast-charge claims need their conditions. Some product pages, including some of ours, mention charging in 1–2 hours. At the currents listed above, that is not consistent with a full 0–100% charge. For comparison, replacing 50% of a 920 Ah pack at 250 A takes about 1.8 hours by the same formula. When any supplier quotes a fast-charge time, ask for:

• The charge current
• The start and end SOC
• The battery temperature
• A charge log

Do not build a shift plan on the quoted time until you have them.

The charger and site supply set the real limit. Delivering 250 A up to the 43.8 V cut-off needs roughly 11 kW of charger DC output. The charger draws more than that from the mains, because of conversion losses and its own consumption. Confirm the AC input rating with the charger manufacturer, then check that your site supply can carry it with every charger you plan to run at once.

If break-time charging is part of your plan, write down how long and how regular those breaks actually are, subtract the time it takes to connect and start charging, then run the formula. If your truck is a reach truck, our 36V reach truck battery selection guide goes model by model through dimensions, weight and current ratings.

Most comparisons between the two chemistries mislead because the numbers were measured under different conditions. The table keeps each figure next to the condition it was stated under, and says so where a condition is missing.

You will see lithium described as lasting a fixed multiple of lead-acid. The published figures above do not support any fixed multiple. A cycle-life number is useful only with its conditions:

• Temperature
• Charge and discharge rates
• Depth of discharge
• End-of-life capacity
• Whether the test was on cells or a complete pack

Ask every supplier for these, us included. Calendar life is a separate question from cycle life: a lightly used battery still ages with time and storage conditions, so ask for both.

How this plays out depends on the operation. The following is our analysis, not a sourced finding:

• One shift, a long overnight charge window, and a charging area and trained staff already in place. Lead-acid's routine already fits the day. The case for lithium rests on the labor and space you would free up, which you need to estimate from your own records.
• Multiple shifts where batteries are currently swapped. Lithium's ability to take charge during breaks can remove the swap, but only if the shift-by-shift energy check above holds.
• Cold or temperature-sensitive sites. The decision turns on charging temperature limits, covered below.

We have left out payback periods and percentage savings. They depend on your labor rates, energy prices, shift pattern and battery prices, and we do not have a like-for-like public source for them. To build your own comparison, cost both options over the same planning period and the same workload, using quotes and your own records for:

• Battery price, plus any approved ballast and installation
• Chargers and any site electrical upgrades
• Energy, including demand charges where your tariff has them
• Maintenance labor and consumables
• Battery swapping time, downtime and spare batteries
• Replacements expected within the period, and end-of-life disposal

Our general lead-acid vs lithium-ion comparison for forklifts discusses these cost categories further.

"Low maintenance" does not mean no checks. The two chemistries need different routines, and in both cases the battery manufacturer's manual is the governing document.

Flooded lead-acid routine

The recurring tasks are watering, equalizing charges, and keeping electrolyte level and temperature in range. Intervals and limits depend on the battery and the charger. Your battery's manual will have its own figures.

As an example of what a manual specifies, an EnerSys manual for one low-maintenance flooded traction series (EnerSys) sets out the following:

• Water quality and timing. Top up with purified water, at or near the end of charge rather than before it. The manual handles very low electrolyte as a separate case.
• Watering intervals. 20, 40 or 65 cycles, depending on the charging configuration. The longest interval applies only with electrolyte circulation and a high-frequency charger.
• Conditions behind those intervals. 80% DOD, five days a week, average 20 °C. The manual notes that multi-shift use or higher temperatures can shorten the intervals.
• Temperature limits. Electrolyte should be below 45 °C before charging starts. 55 °C is an upper limit, not an acceptable working temperature.
• In the US, the charging area itself carries requirements. OSHA 1910.178(g) calls for charging in a designated area with facilities for flushing and neutralizing spilled electrolyte, fire protection, ventilation for gassing batteries, and suitable equipment for handling batteries. It also prohibits smoking and requires precautions against open flames, sparks and arcs in charging areas (OSHA 29 CFR 1910.178).

OSHA's guidance adds that only trained personnel should charge and change batteries, that the truck should be properly positioned and braked before charging or changing, and that eyewash facilities should be able to provide a 15-minute flow (OSHA eTool).

Lithium pack checks

A sealed LiFePO4 pack removes watering and equalizing. What remains is inspection.

An OSHA fact sheet on lithium-ion batteries lists internal short circuits, physical damage, extreme temperatures and improper charging among the causes of thermal runaway (OSHA FS-4480). The fact sheet covers lithium-ion batteries in general, not forklift packs specifically. It still explains what the routine checks are for:

• Catching damage early
• Keeping charging inside the specified limits
• Acting on fault warnings instead of clearing them

For storage, our FL38880 product page recommends a state of charge of 40–60%. Follow the figure in the manual for the pack you actually buy.

A schedule you can adapt

Use this as a starting template and replace the intervals with those in your battery's manual. For both chemistries, only trained and authorized staff should charge or change batteries. Position and brake the truck before charging. The checks below are external inspections. Opening a pack or working on its terminals under load is a job for authorized service personnel only.

For lithium fault codes, use the fault-code table in the manual for your specific pack, and give the recorded code to the supplier when you report it.

Routine safety inspection and maintenance checks on industrial 36V batteries.

Can the existing charger be reused?

Lead-acid to lead-acid. Check the charger against the new battery's capacity and the manufacturer's charging profile.

Lead-acid to lithium. Do not assume the lead-acid charger will work because the voltage class matches. The charger needs:

• The right output voltage and cut-off
• A lithium charging profile
• A current limit inside what the BMS allows
• The right connector
• Often, communication with the BMS

Do not count on energy savings from new charging equipment alone. A 2017 field study funded by the State of Minnesota installed high-frequency chargers on lead-acid fleets and measured 13 charging stations at 9 facilities. It found no consistent reduction in energy per charge. The authors note the small sample. The study also did not control the starting SOC or the energy put back in, so it is not a like-for-like comparison of charger conversion efficiency (Minnesota Department of Commerce / Franklin Energy). If charger efficiency matters to your case, measure AC input against energy delivered and work done at your own site.

Will the truck accept the lithium pack's voltage, current and data?

A truck built around an 18-cell lead-acid battery expects a lead-acid voltage curve. A 38.4 V lithium pack sits in a different window, so the discharge indicator and low-voltage cut-out may need attention.

Current matters as well. Check that the pack's continuous and peak discharge ratings cover the truck's demand. If the truck uses regenerative braking or lowering, check that the pack can accept the current it feeds back.

Some trucks expect battery data from the pack, such as SOC display, interlocks or fault signals. Whether that is needed, and over which protocol and message set, depends on the truck model and controller version. A pack listing CAN or RS485 among its interfaces does not mean it will communicate with a given truck out of the box.

Ask the supplier:

• Which truck models and controller versions the quoted pack has been matched to
• What evidence exists for that match
• What integration work is included

Does a lithium retrofit affect the truck's safety listing?

Ask, do not assume. Different documents prove different things:

• Safety standard certification. A battery certified to a standard such as UL 2580 should come with a certificate or listing record naming the holder and the models covered. UL distinguishes component recognition, which applies only under the conditions of use specified for that component, from a listing of a complete product (UL Solutions). Ask which one the pack has.
• UN 38.3. This is a transport test for lithium battery designs. US rules require a test summary to be made available (PHMSA). It shows the design passed transport tests. It is not a safety approval of the truck.
• CE marking. This is the manufacturer's declaration of conformity with applicable EU requirements, not a safety approval issued by an authority (European Commission). Ask for the declaration of conformity.
• The truck itself. At MODEX 2024, Martin Boyd of Hyster-Yale said that a lithium-powered truck needs UL marks on both the truck and the battery, and advised users to confirm their truck manufacturer's policy through the dealer (MHI). That is one manufacturer's view at an industry event, not a legal ruling, but it shows why the truck side has to be checked separately.

In practice, ask three parties:

1. The battery supplier: certificate or listing record, holder, models covered, and whether it is a listing or component recognition; the UN 38.3 test summary; the declaration of conformity where CE applies.
2. The truck dealer or manufacturer: whether the truck's own listing, approval and warranty remain valid with the proposed battery.
3. Your insurer or safety officer: what documentation they need on file for your country.

Some of our 36V product pages, such as those for the FL38660 and FL38770, list IEC 62619, UN38.3, UL 2580 and CE. A standard named on a product page is not a certificate. Ask us, as you would any supplier, for the document covering the exact model and configuration you are quoting.

Cold affects both chemistries, in different ways.

Lead-acid: usable capacity. Truck manufacturers report a marked loss of usable lead-acid capacity at freezer temperatures (Toyota Material Handling Europe, a vendor of lithium trucks).

Lithium: charging. The published abstract of a laboratory study on small commercial LiFePO4 cells cycled at −18 °C reports marked low-temperature ageing, which the authors link to lithium plating (VTT Technical Research Centre of Finland). The study used 2.3 Ah cells under vehicle-style conditions. It illustrates the risk, but not how a forklift pack with a BMS and heating would behave.

Keep three temperatures separate:

• Ambient temperature: where the truck works and where it is parked to charge.
• Battery temperature: what the BMS measures and uses to allow or limit charging.
• Heating conditions: if a pack has heating, how long it takes to bring the battery into range, how much energy that uses, and what charge current is allowed once it gets there.

Our 36V specifications give a charging range of 0–55 °C. Ask us, and any supplier, which temperature that range refers to.

A truck can often work in a cold zone, but charging a cold battery is a separate question. If trucks will charge inside the cold zone, get the supplier's low-temperature charging limits and heating conditions in writing.

For any multi-shift plan built on charging during breaks, use the battery's SOC records during the first weeks to confirm the shift-by-shift energy check described above.

Sending every supplier the same information is what makes their quotes comparable. For 36 volt forklift batteries, a complete request includes:

• Truck make, model, serial number and controller version, with a photo of the data plate
• Nameplate of the existing battery: voltage, capacity and weight
• Approved minimum and maximum battery weight
• Compartment length, width and height; removal direction; restraint method; cable exit position
• Truck-side connector model, rating and polarity
• The truck's peak current demand and whether it uses regenerative braking or lowering, if the dealer can provide them
• Existing charger make, model and output, and the site's available electrical supply
• Shifts per day, break schedule, typical and heaviest loads, lift height, and any discharge records you have
• Operating and charging temperatures
• Destination country, quantity, and any certification your site or insurer requires

Ask each supplier to return:

• The proposed model, with chemistry, capacity, nominal energy, and continuous, peak and charge current limits
• A drawing with final dimensions, installed weight including any ballast, and connector details
• Written confirmation of charger requirements and of any integration work
• The cycle-life figure with its test conditions
• The certification documents described above
• The maintenance manual
• The formal warranty terms

Our 660 Ah and 770 Ah 36V product pages state a warranty of 5 years or 10,000 hours. Ask for the formal terms that apply to your quoted configuration.