Battery Equipment Charging and Rotation

Purpose

Run the lithium packs as a numbered inventory with a charge state, a temperature history and a measured runtime, so a crew leaves the yard with enough power for the route and the shop never charges a damaged pack.

Battery handhelds fail differently from two-stroke. A trimmer that is out of fuel tells you at the trigger and is fixed in a minute; a pack that has quietly lost half its capacity tells you at the eighth property, with nothing on the trailer to pour into it. That is a route problem, not a tool problem, and it is prevented by measuring runtime rather than by counting packs.

The second reason this is written down is that the failure with real consequences happens in the shop, overnight, unattended. A pack that took an impact, got wet, or was charged outside the temperature window its manual states can go into thermal runaway hours later, in a closed building, and it does not need to be plugged in at the time.

Scope

Covers receipt, inspection, quarantine, charging, numbering and rotation, runtime logging, layup storage, retirement and disposal, and transport of lithium packs and their chargers for handheld and stand-on battery equipment.

Does not cover the bench service of the tools themselves, which the string trimmer and blower service standard owns, or lead-acid starting batteries on mowers, which the small engine seasonal service and storage SOP covers under its own steps. Gasoline and mixed fuel are in the fuel handling and mixed fuel management SOP, and packs are never stored or charged in the same enclosure as fuel.

Roles and responsibilities

Procedure

1. Build the charging station before it holds packs. Non-combustible surface, chargers spaced rather than stacked, nothing stored above them, clear of the exit path, away from fuel containers and from anything that burns. Acceptance: rack in a monitored area with working smoke detection, chargers plugged into a fixed receptacle rather than a daisy-chain of cords. Wrong looks like a shelf of chargers on plywood over the fuel cabinet. Stop rule: if the only space available is against fuel, an exit or stored combustibles, the rack is not built there and packs charge outdoors on a non-combustible pad until a place exists. Hazard: a pack in thermal runaway vents flammable and toxic gas, including hydrogen fluoride, and it cannot be smothered - if a pack smokes, hisses or swells, everyone leaves the building, the fire department is called from outside, and nobody carries it out through an occupied space.

2. Inspect every pack as it comes off the route, before anything is plugged in. Look at the case for cracks and impact marks, the terminals for debris and heat discoloration, and the body for any swelling that makes it sit proud in the tool. Acceptance: case intact, terminals clean and dry, no bulge, no smell, and the pack at a temperature you can hold. Wrong looks like a case seam that has opened slightly, which is a cell venting. Stop rule: any dropped, wet, swollen, hot or odorous pack goes straight to the outdoor quarantine box, on a non-combustible surface away from the building, and never onto a charger; it is written off rather than tested back into service. Hazard: electrolyte from a ruptured cell is corrosive to skin and eyes, so a leaking pack is handled with gloves and eye protection, or not handled at all.

3. Let the pack reach the charging window before it goes on. Acceptance: pack temperature inside the range printed in the manual for your platform, verified by touch and by the charger accepting it without a temperature fault. Wrong looks like a pack straight off an August trimmer going onto a charger warm, or a pack out of a cold truck going on at first light. Stop rule: if the charger throws a temperature fault, the pack waits rather than being cycled on and off until it takes; charging a lithium pack below the manual's minimum temperature plates lithium metal inside the cell, which is permanent and is a safety defect rather than a capacity loss. Hazard: none at this step beyond the handling above, it is a wait.

4. Charge on the matched charger, attended, and take it off when it finishes. Acceptance: manufacturer's charger for that platform, one pack per port, charge completed during a shift when someone is in the building, pack removed from the charger when the indicator says complete. Wrong looks like a rack left running overnight in a locked yard, which is where the unattended fire happens. Stop rule: a charger that runs hot, smells, or shows a fault light is unplugged and tagged out, its packs are inspected before they go anywhere else, and the tag comes off only after the unit is replaced or repaired and has completed one attended charge. Hazard: never charge a pack on a soft surface, in a truck cab, or in a closed toolbox, where heat cannot leave and vented gas collects.

5. Number every pack and rotate first in, first out. Acceptance: a durable number on every pack, the rack loaded so the oldest charged pack leaves first, and every pack in the fleet seeing service rather than three doing all the work. Wrong looks like two favorite packs with double the cycles and four sitting at full charge on the shelf, which ages the shelf packs as surely as use does. Stop rule: an unnumbered pack does not go on the truck, because a runtime log with no pack number cannot retire anything. Hazard: none at this step, it is a labeling job at the rack.

6. Match pack to tool and log runtime against a stated task. Acceptance: runtime recorded in minutes against a named task at a named head or setting, and compared to that pack's own logged runtime when new. Wrong looks like "it does about a day", which conceals a pack losing a fifth of its capacity a season. Stop rule: a pack under 80 percent of its own logged new runtime comes off the route for a controlled bench re-test on that same task, and one that re-tests under the step 8 gate retires there rather than going back in the tote. Hazard: change packs with the tool switched off and the lockout set, and never with a hand near the head - a pack seated into a live switch spins a trimmer head immediately.

7. Store for layup at the charge the manual states, in a stable place. Acceptance: packs at the storage charge the manual names, which for most platforms is a partial charge in the region of a third to a half rather than full or empty, stored dry, cool and out of direct sun, off the ground, terminals covered. Wrong looks like a winter shelf of packs left at full charge, which is the fastest way to lose capacity while doing nothing. Stop rule: a pack that cannot hold its storage charge over the layup is retired rather than carried into spring. Hazard: cold storage is fine and cold charging is not, so packs come up to the manual's window before the first spring charge.

8. Retire on a stated gate, and route what fails it. The shop default is retirement at below 60 percent of that pack's own logged new runtime on the same task, or immediately on any physical defect from step 2, whichever comes first; tune the percentage to your route length. Acceptance: the retirement decision written with both numbers, the new runtime and the current one. Stop rule: a retired or damaged pack never goes in the trash or in a scrap-metal bin - it goes to a battery recycler on their instructions, and damaged or defective lithium cells carry specific packaging requirements under the US DOT hazardous materials regulations at 49 CFR and are forbidden from air transport entirely. Hazard: tape the terminals of every retired pack before it is stored for pickup, because a loose pack shorting against metal in a bin is a fire with nobody watching it.

9. Load packs so nothing shorts, cooks or rides with fuel. Acceptance: packs in their case or a divided tote with terminals covered, out of direct sun, not loose in a toolbox with hand tools, and not in the same enclosure as fuel containers. Wrong looks like four packs rolling in the bottom of a tray with a wrench. Stop rule: a pack that cannot ride with its terminals covered stays at the shop rather than loose in a toolbox. Hazard: a pack's watt-hour rating on its label is what shipping rules key off, so it stays legible; a 56 V pack at 5.0 Ah is 56 x 5.0 = 280 Wh, and that is the number a recycler or carrier will ask for.

The record this produces

• Pack register: pack number, date in service, platform, watt-hour rating, and the runtime measured when new. Read every time a retirement is argued.
• Runtime log: pack number, date, task, minutes. Read by the shop to catch a pack drifting down, and read by the owner to size next season's purchase before the route runs short.
• Quarantine and retirement notes: what happened, who saw it, where the pack went. Read after an incident, and read by the recycler.
• Charger faults, which cluster on one unit long before it fails outright.

Worked pass: Thursday close-out, seven packs on the rack

The fleet is seven packs, numbered 1 through 7, all on one platform.

Step 2: packs 1, 2, 3, 4, 5 and 7 pass inspection. Pack 6 fails step 2 - the case is slightly proud along the seam and the pack is warmer than the others 40 minutes after it came off the trimmer. Stop rule taken: it goes to the outdoor quarantine box on the concrete pad, not on a charger, and it is not opened, tested or brought back inside to see whether it settles.

Step 3: the six remaining packs sit 25 minutes until they are at hand temperature, and every charger accepts them without a temperature fault.

Step 6, the runtime log for pack 4, measured on the same task each time, string trimming at the standard head: new baseline 44 minutes, today 24 minutes. That is under the 80 percent bench-re-test trigger, so it goes to the bench, and the controlled re-test returns the same 24 minutes.

Step 8 fires on pack 4. The gate is 60 percent of that pack's own baseline, and 60 percent of 44 minutes is 26.4 minutes. Today's 24 minutes is under 26.4, so the pack retires. Both numbers go on the retirement line, its terminals are taped, and it joins pack 6 in the recycler bin rather than the scrap steel.

That leaves the count for tomorrow: 7 packs less pack 4 retired and pack 6 quarantined is 5 serviceable. The route runs three trimmers and the standard is two packs per trimmer, so it needs 3 x 2 = 6 and is one short. The crew lead is told tonight rather than at the second property, and one trimmer goes out as the mixed-fuel unit under the fuel handling SOP.

Step 9: the five serviceable packs go in the divided tote with terminals covered, in the cab rather than beside the fuel cans on the trailer.

Two packs came off the rack tonight and neither did it silently. The shop knows why, the recycler will take both, and the owner has a purchase decision with two dated numbers behind it instead of a complaint.

References

• Manufacturer manuals for your battery platform: charging temperature window, storage charge, charger pairing and pack ratings. These are platform-specific and the manual governs.
• US DOT hazardous materials regulations at 49 CFR for transport of lithium cells, including the separate requirements for damaged, defective or recalled packs.
• Your battery recycler's acceptance instructions for terminal protection, packaging and quantity.
• See related: the LawnCare string trimmer and blower service standard, fuel handling and mixed fuel management, and small engine seasonal service and storage.