The technical groundwork, written by the engineers who build the packs.

A pack that will not charge is usually in protection, not failed. The three common causes are the BMS holding a protection state after an over-discharge or over-temperature event, an open circuit between pack and charger, and a charger that is faulty or connected with reversed polarity.

Check in this order. Re-seat the pack connector to clear the protection latch, verify every terminal is tight, confirm the charger polarity matches the pack, then measure the charger's output with a multimeter to confirm it is delivering voltage at all.

One pattern is worth recognising: a pack reading 49 V where a full 13S NMC assembly should read 54.6 V, with the charger relay clicking but no current flowing. That is almost always one or more weak strings inside the pack holding the BMS in protection — a pack-level fault, not a charger fault.

Charging that terminates below the cut-off voltage almost always means the strings inside the pack disagree on state of charge or on capacity. Whichever string fills first reaches the protection threshold and stops the whole charge, leaving the rest short.

What to do. Recharge with an equalising charger so every string is brought to the same voltage. If the capacity spread is large, the divergent cells have to be replaced — equalisation cannot recover capacity that is not there. The permanent fix is at assembly: cells should be capacity-tested and matched before a pack is built.

Four symptoms show up before a BMS fails outright: voltage swinging by more than ±1 % while running, cell-to-cell deviation above 0.1 V, status data that can no longer be read, and protection tripping often enough to cause repeated shutdowns.

Any one of these warrants a check by a qualified technician before the pack is put back into service. The failure mode is gradual — a degrading sampling circuit or balance path first produces bad readings, and only later produces bad behaviour.

Open-circuit deviation between cells should stay under 0.05 V, and deviation under load or charge under 0.1 V. Those are the acceptance figures for a healthy pack.

When to act. Above 0.2 V the pack is seriously unbalanced and needs an equalising charge. Above 0.3 V the BMS may refuse to charge or discharge at all. If one cell's deviation from the rest keeps widening, that cell is ageing faster than its neighbours and should be replaced.

Fault codes are read over the CAN bus with a reader, or through the manufacturer's app. The five that account for most events: over-voltage (a cell above 4.2 V for NMC or 3.65 V for LiFePO4) — check the balance circuit; under-voltage (below 2.5 V NMC or 2.0 V LiFePO4) — charge immediately, and if it recurs the capacity is no longer sufficient; over-temperature (above 60 °C) — stop and inspect the cooling path; over-current — check whether the truck is being operated beyond its duty rating; and communication fault — inspect the CAN wiring.

Many BMS units clear a fault automatically once the condition passes. A code that returns repeatedly is telling you the underlying cause has not been addressed.

Three tests separate them. Measure the cells directly — if the cells are all normal but the BMS reports otherwise, the BMS is at fault. Bypass the BMS — if the pack then charges and discharges normally, the BMS was the limit; if the problem persists, it is in the cells. Read the code — communication and sensor errors point at the BMS, while over-voltage, under-voltage and excessive deviation point at the cells.

A restart is the quickest tie-breaker: a BMS fault may clear on power-cycle, a cell fault will not. BMS faults are usually resolved by a reset or a firmware update; cell faults require physical replacement.

The BMS log is the pack's flight recorder and needs a CAN reader to decode. Six fields carry most of the diagnostic weight. Highest cell voltage — should stay at or below 3.65 V on LiFePO4; persistently high points to low capacity or high internal resistance. Lowest cell voltage — should stay at or above 2.5 V; persistently low points to self-discharge or a micro-short. Cell deviation — static under 0.05 V and dynamic under 0.1 V, with anything above 0.2 V indicating serious imbalance. Peak temperature — under 50 °C normal, above 60 °C a thermal-risk indicator. Cumulative throughput against design capacity — a fall of more than 30 % marks end of life. Cycle count against rating.

As a worked example: a 24 V-class 200 Ah pack at 1,200 cycles and roughly 80 % state of health that no longer runs a six-hour shift has reached replacement, even though nothing has visibly failed.

Inaccurate SOC is normally a coulomb counter that has drifted, or cells that have gone out of step. LiFePO4 makes this worse than other chemistries: its discharge plateau is almost flat between 3.2 V and 3.3 V, so voltage alone cannot tell you how full the pack is. The BMS therefore integrates current over time, and that integral accumulates error.

Full-charge recalibration. Charge until the charger stops on its own. The BMS re-ties the SOC curve to the voltage curve at the top of the range. A pack that is never taken to full will keep drifting.

Deep-cycle recalibration. Run one complete 0–100 % cycle; on LiFePO4 three of them restore accuracy. A pack that reads 80 % and dies at 30 % is the classic case, and three full cycles fix it.

A cell that reaches the protection voltage first on charge and falls slowest on discharge is either low on capacity, high on internal resistance, or being misreported by the BMS.

Low capacity behaves like a small bucket: it fills fast, so its voltage climbs first. High internal resistance shows a falsely high voltage under charge from the IR drop, which falls back once the pack rests. A sampling fault is confirmed by comparing the BMS reading against a multimeter at the cell terminals. A failed balance path is confirmed by watching whether balancing ever starts on that string.

If the deviation exceeds 50 mV and equalisation will not correct it, the cell should be replaced — and the replacement must be matched on both capacity and internal resistance, joined with a spot welder to keep the connection resistance low.

On a 48 V-class pack, full charge is 54.4–54.6 V; under normal load it should hold 46–54 V; below 44 V it is critically discharged, and below 40 V severely so. Per cell, the corresponding LiFePO4 figures are 3.40–3.65 V at full, 2.9–3.4 V under load, and below 2.8 V or 2.5 V at the two discharge thresholds.

The diagnostic point is that the pack must stay inside 46–54 V while working. An open-circuit reading below 46 V means something is wrong, and a cell spread beyond 0.05 V static or 0.1 V dynamic means the pack is out of balance.

For daily work, keep it high. Recharge as soon as it drops below 20 % — deep discharge costs cycle life. Over-charging and over-discharging are both prohibited.

Below 0 °C, do not charge. Charging a lithium pack in freezing conditions deposits lithium irreversibly on the anode. If the pack has been out in the cold, let it come back above 5 °C before connecting the charger.

Charging below freezing deposits metallic lithium on the anode instead of intercalating it. The consequences are cumulative and partly irreversible: lithium dendrites can pierce the separator and cause an internal short; a single charge at 0 °C can cost 2–5 % of permanent capacity; and repeated cold charging raises internal resistance by 20–30 %.

The rule is absolute. Do not charge below 0 °C. Where cold operation is required, specify a pack with integral self-heating — our cold-store variants operate to −20 °C. A pack brought in from the cold must be allowed to reach 5 °C before charging.

Usually protection, and correct behaviour. The BMS is told not to charge below 0 °C precisely because of the lithium-plating risk above, so a refusal in freezing conditions is the pack doing its job.

Confirm it. Read the BMS temperature data. If the temperature is genuinely below 0 °C, this is normal protection. If it is above 5 °C and the pack still will not charge, then suspect a failed temperature sensor or a BMS logic error and have it checked.

Move the pack indoors and let it come back above 5 °C. For sites that run cold routinely, specify a self-heating pack rather than fighting the protection.

A pack that is hot to the touch during charge or discharge has either a high-resistance cell or a partial internal short. Both are dangerous if left in service, and neither improves on its own.

Stop using the pack immediately. It needs to be examined by a qualified technician, who will identify and replace the offending cells or repair the affected wiring. Continued operation at elevated temperature is how a repairable fault becomes a thermal event.

Store at 40–60 % state of charge — that is the best storage point. Storing at full charge or at deep discharge both accelerate capacity fade.

The environment should be dry, cool (15–25 °C is ideal) and free of corrosive gases. Check the state of charge every three to six months, and if it has fallen below 20 %, bring it back up to 40–60 %.

No — not under any circumstances. Swelling means gas is being generated inside the cell, and the usual causes are over-charging (electrolyte decomposition above the voltage ceiling), sustained over-temperature, or an internal short from separator damage.

What to do. Stop using it immediately and isolate it in a fire-rated container (UL 94 V-0 or better). Keep people 10 m clear. Have it handled by a qualified technician — do not open it.

The reason for the caution is that a swollen lithium pack can enter thermal runaway at any moment. It does not have to be in use to catch fire.

Never water. Water conducts, and on a live pack it can intensify the short. Use a dry-powder extinguisher, a CO2 extinguisher, or fire sand to smother it.

After the flames are out, keep watching. A pack in thermal runaway can reignite. Any sign of leakage, smoke or deformation means the pack comes out of service immediately and the area is cleared.

Two causes account for most mid-shift shutdowns. The first is low voltage: the pack reached the protection board's or the controller's lower limit and protection opened. The second is over-current: a heavy start or a ramp drew more than the board's design current and tripped over-current protection.

Recharging resolves the first; a restart resolves the second. If either recurs, look at whether the truck is being worked beyond the duty cycle the pack was specified for — repeated protection events are a sizing signal, not a nuisance.

Three candidates, in order of likelihood: the pack was not fully charged; one string has diverged in voltage or capacity from the rest; or the pack has a micro-short or elevated self-discharge.

Recharge fully and repeat the test first — that rules out the trivial cause. If the range is still short, a technician needs to measure the individual string voltages and replace the cells that have diverged.

A battery in heavy use — five shifts a week or more — should be checked weekly; lighter duty every two weeks. Water demand rises by around 30 % in summer.

Timing matters as much as frequency. Water only after the battery is fully charged and has cooled for four hours. Electrolyte expands during charging, so topping up early causes it to overflow.

Standards. Use distilled or deionised water only — never tap water. Fill to roughly 6–15 mm above the plates. Watering after charge avoids diluting the acid.

Four signs: the plates are exposed above the electrolyte on inspection; the truck's voltage sags noticeably under load; the battery overheats repeatedly; or the level is less than 6 mm above the plates at the weekly check.

If a refractometer is available, measure the electrolyte specific gravity. Below 1.220 the acid is too weak, and the water-to-electrolyte balance needs looking at rather than simply adding more water.

Sulphation is what happens when a lead-acid battery is left part-discharged: hard lead sulphate crystals form on the plates, cutting capacity by 20–40 % and raising internal resistance.

Treatment by severity. Light sulphation responds to an equalising charge (15.5 V for a 12 V battery). Moderate sulphation needs a low-current charge. Severe sulphation requires a water-treatment process by a specialist.

Prevention is cheaper than all three. Recharge within 24 hours of use, never leave the battery stored below 50 % state of charge, and run an equalising charge once a month.

Stratification is gravity at work inside the cell: the denser acid sinks to the bottom and the weaker electrolyte stays at the top. The upper and lower parts of the plate then work at different concentrations, and the plate corrodes faster as a result.

Correction. An equalising charge is the standard remedy — once a month, at 56.4 V on a 48 V system — because the gassing it produces stirs the electrolyte and mixes it back together. A technician can also agitate the electrolyte mechanically with the right tool.

Prevention. Avoid prolonged low-current charging, and run a full charge-discharge cycle periodically.

Around 2 % a day is normal. As a reference, a 48 V 500 Ah battery left to stand for a week after a full charge will typically lose 1.5–2 V — that is expected behaviour, not a fault.

What is not normal. A drop of more than 0.5 V in 24 hours points to external leakage or an internal micro-short. And if one cell self-discharges noticeably faster than its neighbours, that cell has either contamination or a damaged separator.

Check whether the battery top is dirty — contamination creates a leakage path across the lid. Clean it. A cell that is genuinely faulty needs a technician.

Equalising is the maintenance step that removes plate sulphation and mixes stratified electrolyte back together.

Method. Set the charger to its equalising mode — 15.5 V for a 12 V battery. Charge at a small current, one tenth to one twentieth of the normal rate, and extend the charge by two to four hours. Watch the temperature throughout; it must not exceed 45 °C.

Frequency. Monthly for normal use. For high-intensity operations running two or more shifts a day, after every ten ordinary cycles. If capacity has visibly dropped, run one or two equalising charges back to back.

Electrolyte temperature must not exceed 45 °C during charging. Above that the penalty is steep: 50–55 °C halves service life and accelerates plate corrosion; above 60 °C there is a thermal-runaway risk, plates warp, and a fire becomes possible.

Response. If 45 °C is exceeded, stop the charge and let the battery cool for two hours before continuing. If it happens repeatedly, check three things: charger voltage too high, charge current too high, or the battery is short of water.

A temperature sensor interlocked to automatic load reduction is worth fitting wherever charging runs unattended.

That is terminal corrosion, produced by acid seepage reacting with airborne hydrogen. It matters because it can raise the connection resistance to around 200 mΩ, which turns into heat under high-current discharge.

Cleaning. Disconnect the battery. Make a paste of baking soda and water and apply it to neutralise the acid. Scrub with a brass brush. Rinse with distilled water and dry thoroughly. Then apply a corrosion-inhibiting gel or dielectric grease.

After cleaning, measure the cable resistance with a milliohm meter — above 5 mΩ, replace the cable.

Three tests, used together. Voltage: a healthy cell rests at about 2.1 V, so a cell below 1.8 V has failed. Specific gravity: after charging, below 1.225 indicates the cell has sulphated. Internal resistance: measured with a resistance tester, a reading well above the normal band for that cell's capacity means failure — the reference table further down gives the bands.

No single test is conclusive on its own. A cell can hold voltage and still have lost its capacity, which is why resistance and specific gravity are read alongside it.

Measure each cell after the battery has been fully charged and left to rest for two hours; a healthy cell reads about 2.1 V.

Failed: below 1.8 V, indicating sulphation or an internal short. Unbalanced: a spread of more than 0.2 V between cells. Suspect: a cell that produces no gassing, or only weak gassing, while the others gas normally after charging — that points to an internal short.

Worked example: a 48 V lead-acid pack is 24 cells in series, and a healthy cell rests at about 2.1 V, so a healthy string rests at about 50.4 V. If one cell reads 1.5 V, the remaining 23 cells still total 48.3 V and the string still reads 49.8 V — 0.6 V, about 1.2 %, below a healthy string, and still above the 48 V nominal. A failed cell is found by measuring cell by cell: at 1.5 V it sits below the 1.8 V threshold and is replaced.

This is the classic false-voltage symptom: normal open-circuit voltage that collapses the moment a load is applied. The root cause is excessive internal resistance.

Diagnosis. Measure each cell's resistance — above the normal band for its capacity, and particularly more than 30 % above it, the battery is seriously aged. Then load-test: apply a load such as a 50 A resistor for ten seconds and watch the sag. A healthy battery drops no more than 2 V; more than 3 V confirms excessive resistance.

Where the resistance comes from. Plate sulphation from chronic undercharging, electrolyte stratification, grid corrosion reducing the conductive cross-section, or a poor weld or corroded joint between post and busbar.

Remediation. A rise under 20 % can be treated with a pulse desulphator over about 48 hours. A rise above 30 % means the failed cells should be replaced. Either way, check and tighten every connection and apply conductive paste.

Internal resistance is the single most informative indicator of a lead-acid battery's condition, because it reflects grid corrosion, sulphation and water loss before they show up as lost runtime.

Methods. A dedicated resistance tester connected across a cell's terminals; the AC injection method, which injects a 1 kHz signal and computes resistance from the response; or DC discharge, which applies a brief high current and measures the voltage drop.

Reference limits by capacity. 200 Ah: normal below 5 mΩ, act above 6.5 mΩ. 500 Ah: normal 3–5 mΩ, act above 6.5 mΩ. 1,000 Ah: normal 2–4 mΩ, act above 5.2 mΩ.

Reading the trend. A rise of 10–20 % is light sulphation and may respond to pulse treatment. A rise of 20–50 % suggests moderate sulphation or corrosion and the cell may need replacing. Beyond 50 %, the plates are badly sulphated or the active material has shed, and repair is rarely worthwhile.

Compare readings at the same temperature — resistance falls as temperature rises, by roughly 2 % per 10 °C.

In a series string, the same current passes through every cell, so a mismatch guarantees that some cells are mistreated. A small-capacity battery in the string will be over-charged on the way up and over-discharged on the way down, shedding active material from its plates. A large-capacity battery never reaches full charge and sits chronically undercharged, which accelerates sulphation. Mixing old with new is the same problem in one step: the older, smaller battery becomes the bottleneck and the new one never performs to its rating.

The same rule applies to lithium: never mix new and old packs. A capacity mismatch amplifies imbalance within ten cycles and starts tripping BMS protection.

Yes, and it is one of the most common conversions we quote. Four things have to be checked first.

Voltage. Confirm the pack's voltage matches the truck's system. Note that a truck described as 48 V is a lead-acid rating — the lithium equivalent is 51.2 V, 16 cells in series. Charger. A lead-acid charger will not charge a lithium pack; the charger must be replaced with a lithium-specific unit. Compartment. A lithium pack is 30–50 % lighter, so ballast or revised mounting may be needed to keep the truck's stability and counterweight correct. Communication. Some trucks expect to talk to the BMS over CAN, which may require fitting a communication module.

No — never. The two chargers follow different profiles. A lithium charger runs constant current then constant voltage (CC-CV), holding a fixed upper voltage. Lead-acid needs a bulk stage followed by an absorption stage, with a different voltage trajectory.

Running the wrong profile damages both the battery and the charger, and it does so quietly: the battery may appear to charge while sulphating or gassing abnormally.

The requirement differs by chemistry. Lead-acid: acid-resistant gloves (colour-coded red), ANSI-rated goggles plus a face shield when watering, a flame-retardant apron to ASTM F696 at 0.5 mm, steel-toe boots, and ordinary hand tools. Lithium: insulating gloves rated above 1,000 V, ANSI-rated goggles, flame-retardant clothing, steel-toe boots, and insulated tools.

Colour-code the gloves — red for acid, blue for lithium — so the two are never crossed. Replace them every 30 shifts, and immediately on any damage.

Ventilation. Lead-acid charging evolves hydrogen, so the area needs at least 100 cfm of extraction. Lithium charging needs heat removal rather than gas extraction, at 50 cfm or more. Fit a hydrogen detector that alarms at 1 % concentration — above 4 % there is an explosion risk.

Electrical. Charging areas need Class I Division 2 rated outlets, a ground-fault circuit interrupter at 30 mA sensitivity, and one metre of clear space around every charger.

Fire provisions. Keep baking soda beside lead-acid batteries — 5 kg to neutralise each litre of electrolyte. Keep a Class D extinguisher or fire sand beside lithium. An eyewash station and a first-aid kit belong in the area either way.