The Battery Charging Station SOP

Purpose

A shop with ten techs can easily have sixty or more lithium-ion tool packs moving through it, and most of them are charged wherever there happens to be an outlet: a workbench, the parts counter, a power strip on the floor behind a stack of boxes. A pack that was dropped off a ladder last week can look normal and go into thermal runaway (a self-feeding internal heating that ends in venting, fire, or both) on a charger at 2 am with nobody in the building. This procedure puts all charging in one prepared place, makes every pack pass a look before it goes on a charger, takes damaged packs out of circulation the moment they are found, and says what happens to the station at the end of the day.

Scope

Covers lithium-ion and other rechargeable packs for cordless tools, work lights, test instruments and small equipment charged at the shop.

Does not cover handling a pack that is already damaged, swelling, hot or venting, which follows 'The Damaged Lithium Battery Handling SOP'; this procedure hands off to it at a named step. Does not cover choosing and building the station (see related: Setting Aside a Battery Charging Area), lead-acid forklift and floor-machine batteries, which are charged under their own rules for hydrogen and acid, or charging in the vans.

Roles and responsibilities

Procedure

1. Charge only at the station. Bring packs to the marked station: a metal shelf or cabinet, its own outlets, a smoke detector above it, nothing combustible stored on or within the marked area, and not in front of an exit or the flammable cabinet. Acceptance: every charger in the building is at the station, plugged into a station outlet or a listed strip that is not plugged into another strip. Wrong looks like a charger on a bench, in a truck cab or on cardboard; unplug it and bring it to the station, and tell the shop lead so they find out why it was there (usually the station is full, which is a capacity finding, not a discipline one). Hazard: do not unplug a charger with a hot or swollen pack on it by pulling the pack; unplug at the wall and go to step 6's stop rule.

2. Look at every pack before it goes on a charger. Turn it over in your hand. Acceptance: case flat and uncracked (set it on the shelf: it sits without rocking), no bulge at the seams, no scorch marks or melted plastic, terminals clean with no green or white crust, and it has not been dropped from height, run over, or soaked since it was last charged. Stop rule: any one of those is a failed pack. It does not go on a charger and it does not go back in the bin of good packs. Put it in the damaged-pack bin at the station under The Damaged Lithium Battery Handling SOP, tape over its terminals, and write the date and "dropped", "swollen" or "cracked" on it with a marker. Hazard: a swollen or cracked pack can vent when pressed; do not squeeze it to check, and wear safety glasses at the station.

3. Match pack, charger and cord. Use only a charger from the same tool system as the pack, carrying a recognized testing laboratory's listing mark, with its cord and housing intact. Acceptance: same system, listing mark present, no cut, crushed or taped cord, no cracked housing. Wrong looks like an off-brand adapter, a charger from another system "that fits", or tape on a cord; the charger comes out of service with a red tag and goes to the shop lead. Hazard: a charger with damaged insulation is a shock hazard before it is a fire hazard; unplug it at the wall by the plug, not the cord.

4. Let the pack come to room temperature first. Packs straight from a van parked in summer sun, or from an unheated truck in winter, wait on the station shelf (off the charger) until they feel neither warm nor cold to the hand, commonly 30 to 60 minutes. Acceptance: pack at room feel, and the charger shows a normal charging light, not a temperature fault. Charging lithium-ion below freezing can plate metallic lithium inside the cell and leave it damaged without any outward sign, and most tool chargers refuse a pack that is too hot or too cold; if the charger shows its temperature fault, that is the charger doing its job. Stop rule: never defeat or work around a temperature fault by swapping chargers or warming a pack with a heat gun; set it aside to come to temperature.

5. One pack per charger, nothing on top. Seat the pack fully, with the charger flat on the shelf and its vents clear. Acceptance: charging light on, pack fully seated, nothing stacked on the pack or charger, at least the spacing the station is marked for between chargers. Wrong looks like packs stacked on chargers to save shelf space, or a rag laid over a charger; clear it. Hazard: a blocked charger runs hot and can fail the pack it is feeding.

6. Check on it, and know the stop rule. About halfway through a normal charge, or before you leave the area, glance at the station. Acceptance: packs and chargers warm at most, no smell, no sound, lights behaving normally. Stop rule: a pack that is hot to the hand, hissing, popping, swelling, smoking or giving off a sweet or chemical smell is not touched. Unplug the charger at the wall if you can do it without reaching over the pack, move people away, open the nearest bay door, and follow The Damaged Lithium Battery Handling SOP. If the pack is smoking or burning, leave it, evacuate the area under the emergency action plan, and call 911 from outside; do not carry it out, because a cell can flare while you are holding it. Hazard: battery smoke is toxic; nobody stays in the room to watch it.

7. End of day: unplug, unless the station is built for overnight charging. The last person out switches off the station outlets or unplugs every charger and initials the close log. Acceptance: no charger energized and the station's switched outlet or indicator off, initialed with the time. The exception is a station the shop manager has designated in writing as an overnight station: inside a noncombustible cabinet or enclosure, with smoke or heat detection that reports to a monitored alarm, and on a timer that cuts power at a set hour. Only that station may stay on, and it carries a sign saying so. Wrong looks like chargers left on at an ordinary station; switch them off, and log it for the shop manager. Hazard: before switching off, glance at every pack for step 6's signs; the end-of-day pass is the last look anyone gets until morning.

8. Move charged packs off the chargers. Packs that read full go back to the van kits or the charged-pack rack, not left on chargers overnight or for days. Acceptance: no full pack sitting on a charger at close. Wrong looks like the same pack on a charger for a week; it goes back into circulation or to the shop lead if nobody claims it.

9. Empty the damaged bin on schedule. The shop lead checks the damaged-pack bin weekly: a metal container with a lid, kept at the station or outside where the battery SOP puts it, holding the sand or other material that SOP specifies. Acceptance: every pack in it taped and dated, nothing else in the bin, bin no more than half full. The shop manager arranges recycling through a battery recycler, which will give packing instructions, because shipping damaged lithium batteries is regulated under federal hazardous materials rules and a cracked pack cannot go in an ordinary box. Hazard: never put a damaged pack in the trash or the scrap metal pile; garbage trucks and scrap yards catch fire from exactly this.

10. Weekly station check. The shop lead initials a short check: detector present and its test indicator working, outlets and strips undamaged, no combustibles in the marked area, chargers counted against the station list, close log initialed every working day. Acceptance: all items checked and initialed. A missing close-log initial is asked about the same week; a pattern of missing initials is the shop manager's.

The record this produces

The daily close log at the station (date, time off, initials); the weekly station check sheet; and the damaged-pack log (date found, who found it, why, date bagged, date picked up by the recycler). The shop manager reads the damaged log monthly: three packs from the same van in a month says that van's storage or a tech's handling needs looking at. After a fire, the insurer's investigator and the fire marshal will ask where packs were charged and whether the station was on overnight; the close log answers that.

Worked pass

Thursday, July. A tech brings 6 packs in from a van that sat in the lot all afternoon.

• Step 1: at the station. Pass.
• Step 2: 5 packs sit flat and look clean. The sixth rocks on the shelf, with a seam visibly opened at one end. Fails. The tech does not press on it, tapes the terminals, writes "swollen 7/17" on it, sets it in the damaged bin and tells the shop lead. 5 packs continue.
• Step 3: chargers matched and listed, cords good. Pass.
• Step 4: all 5 packs feel warm from the van. Wait on the shelf about 45 minutes. One charger then still blinks its temperature fault on the first pack tried; the tech leaves that pack off for another 15 minutes and it then charges. Pass after the wait.
• Step 5: one pack per charger, 5 chargers. Pass.
• Step 6: checked at 5:10 pm, chargers warm, packs warm, no smell. Pass.
• Step 7, 5:45 pm: last person out sees 2 chargers still showing charge lights. This is an ordinary station, not an overnight one. The two packs are left on the shelf, partly charged, outlets switched off, close log initialed 5:47 pm.
• Step 8: 3 full packs to the charged rack. The 2 partial ones finish in the morning.

The damaged log now shows a second swollen pack from the same van this month, which is the shop manager's question for the tech on Friday: where in the van do the packs ride, and do they sit in the sun.

References

• See related: The Damaged Lithium Battery Handling SOP; Setting Aside a Battery Charging Area.
• The tool manufacturer's battery and charger manual for temperature limits and charger compatibility.
• US DOT hazardous materials regulations (49 CFR Parts 171 to 180) as they apply to shipping damaged lithium batteries, through the recycler's instructions.
• See related: How to Write a One-Page Emergency Action Plan.